Answer:
5/18
Step-by-step explanation:
There are two ways this can happen: you roll a 3 on the first cube and not a 3 on the second cube, or you roll not a 3 on the first cube and 3 on the second cube.
P = (1/6)(5/6) + (5/6)(1/6)
P = 5/36 + 5/36
P = 10/36
P = 5/18