Question

Given : ab = 8a b + d = 20 Prove : d = 12

Answer 1

We have:

$ab=8a(1)$$b+d=20(2)$

In order to prove that d=12, we do as follows:

$ab=8a\Rightarrow b=\frac{8a}{a}\Rightarrow b=8(3)$

Now, replacing (3) on (2), we have:

$8+d=20\Rightarrow d=20-8\Rightarrow d=12(4)$

And is proven that d=12.