1 is not suff

K>35

36+5 = 41
40+ 5 =45

so the tens digit of k has two values 3 and 4 ..insuff

2 is suff
units digit can be 6,7,8,9
so only 3 can be the tens digit to satisfy the stem

36+5
37+5
38+5
39+5
all of the above give 4 as the tens digit(as stated in the stem)

if you use 4 as the tens digit with 6,7,8,9 as units digit, it contradicts the stem since k+5 has tens digit of 5.

B

For the first one, take 2 samples --

I. x = y = z = 3
II. x = y = 3, z = 4

1 - insufficient. Works for I but doesn't for II

2 - insufficient. Works for I but doesn't for II

1 and 2 together, same story, works for I but doesn't for II

Hence E

10s digit of k + 5 = 4. How do we represent this as a formula?

Say k = 10 * t + 1 * u

10*t + 5 = 4