Another way to look at it is algebraically.
We can model the question as is x + 10y + 100z < 550?
x being the units digit
y being the tens digit
z being the hundreds digit
(1) we are given xyz = 30
Then factors of 30 are: 1,2,3,5,30
choosing some examples:
if z=5, y=3, x=2 then the answer is yes
but if z=6, y=5, x=1 answer is no
Insufficient
(2) we are given x + y + z = 10
choosing some examples:
if z=8, y=1, x=1 answer is yes
but if z=1, y=8, x=1 answer is no
Insufficient
Taking the two together, from (1) the only factors which fit (2) are 5,3,2 therefore (as georgeung said) we know x + 10y + 100z < 550 is true because no matter how you arrange the factors they are always less than 550.
Sufficient
C
