Answer:
5/16
Explanation:
Each number can happen in exactly one way (one sets the digit of tens and the other of ones).
We know that the law of divisibility by 3 is "sum of digits has to be divisible by 3", so let's examine the numbers:
11
13
15 - Yes
17
31
33 - Yes
35
37
51 - Yes
53
55
57 - Yes
71
73
75 - Yes
77
So it's 5 out of 16 options.
We could do it by examining the relation and modulus shifts with each digit, but for 16 numbers it's seriously faster to just list them.