AB is the same as A multiplied by B. In order to get this value, we need to figure out the value of A and B.
We have two equations here:
a + 5b = 2b + 13
a = 3b - 5
The second equation already has A isolated. So, we can take that equation and plug in the value for A. Doing so will allow us to solve for B.
(3b - 5) + 5b = 2b + 13
8b - 5 = 2b + 13
6b - 5 = 13
6b = 18
b = 3
Now that we know B, we can use our equation that isolated A.
a = 3(3) - 5
a = 9 - 5
a = 4
Therefore, a = 4 and b = 3, and ab = 12.
Hope this helps!