ab = 2a + 3b + 5
ab - 2a = 3b + 5
a (b - 2) = 3(b - 2 + 2) + 5
a (b - 2) = 3(b - 2) + 3*2 + 5
(a - 3) (b - 2) = 11
Now put a - 3 as 1,-1,11,-11 and b - 2 as the other factor and get the integral values
Eg. Put a - 3 = 1 and thus put b - 2 = 11. So you get a = 4 and b = 13.