Answer:
27
Step-by-step
B = A + 5
10A + B = 3(A + B)
for your equations.
Let's replace the Bs in the bottom equation with A + 5s, because we know that's the same thing from the top equation.
10A + A + 5 = 3(A + A + 5)
11A + 5 = 3(2A + 5) careful when you distribute the 3 here
11A + 5 = 6A + 15
5A = 10
A = 2
Then we know that B is 5 more than that, so B = 7.
Your number is 27.
We double check this and see that the 7 is five more than the 2. 27 is three times what we get when we add the digits (2 + 7 = 9).
