Question 878856
A = B + 4
A + 7 = 2B
Substitute the known value of A from the first equation into the second.
(B+4) + 7 = 2B
Add
B + 11 = 2B
Subtract B from each side.
11 = B
.
If B is 11, then A must be 4 more, or 15.
15 + 7 is indeed twice 11.
Success!