I just need to know if they have equivalent volumes and an explanation.

Answer: Yes, they have equivalent volumes.
Step-by-step explanation:
For the volumes to be equal, a would have to be equal to b. We'll assume x=x
1. Set the volumes equal to each other
x +a +2b =x +2a +b
2. Simplify
[x +a +2b =x +2a +b] -x
[a +2b =2a +b] -a
[2b =a +b] -b
b =a
Therefore, 2a=2b, a=b, and x=x
Since the two prisms have the same measurements, they have the same volumes.