Solution:
Let the part which is residential be x and let the other part be y.
We need to know whether x > y or not.
Consider first (1) alone.
We just get that y is commercial.
Obviously, it is not sufficient alone because we do not know how much part is residential and how much part is commercial.
Next consider (2) alone.
We only come to know that x can become 3x which will be less than total land area but we do not come to know whether x > y or not.
Next combine both the statements together and check.
On combining we get that total land area is x + y where x is residential and y is commercial.
Now since x can become 3x, we will have that 3x <= x + y.
Or 2x <= y.
Since x and y are positive, we conclude that x < y.
So most of the area is not residential.

The correct answer is (C).

Night reader wrote:I have just made minor edition my solution which does not change approach. Below I would like to test my solution as Rahul came with C and I find E as the only possible choice.

question: call residential R and Commercial C, then is R>C?
st(1) precisely gives that R+C=Total Lands i.e. only R and C in the set are present; we need the relationship between R and C. Not Sufficient.
st(2) precisely gives that R could become 3*R then C must be C-2*R; again missing the relationship between R and C, as it's possible 3*R < or > or = (C-2*R), moreover we don't what are the other parameters in the set (e.g. some D or F...) Not sufficient.

Combining st(1&2) Not sufficient.

testing for choice C with 2 alternatives:
1) suppose initially R=2 and C=9, then after changed proportion 3*R or 3*2 and C-2*R or 9- (3*2) => new R=6 and new C=5 => R>C because 6>5
2) suppose initially R=2 and C=11, then after changed proportion 3*R or 3*2 and C-2*R or 11- (3*2) => new R=6 and new C=7 => R<C because 6<7

Therefore, we need relationship between R and C to decide if R < or = or > C

But we need to know whether original value of R is more than original value of C or not.
In 1) R=2 < C=9 and 2) R = 2 < C = 11.

In both case it is not.

Woozler wrote:Even after Rahul's explanation I still don't get it why it's not (B). If land zoned residential could be tripled then it means that only one third or less of all land in city A is currently zoned residential.

.

Just consider statement (2) alone.
It means that there can be a third type of area apart from residential and commercial.
Suppose initially residential area R is 8, commercial area C is 2 and some other part say X is 36.
Next if R can be tripled, we can have that R is 24, C is 2, and X is 20.
Here originally R > C.
Now suppose R is 5, C is 6, and X is 36.
If R can be tripled, we can have that R is 15, C is 6, and X is 26.
Here originally R < C.
So from (2) alone nothing definite can be said whether R > C or not.