G(x)=8(x-3)-7
The number in the parentheses has to be changed to positive 3.
You keep the number (-7) the same sign it already is. The vertex is (3,-7)
Assuming we have parallel lines, we can solve for x.
Since a = 3x - 10 (vertically opposite angles are equal),
3x - 10 = 2x + 15 (alternate angles are equal)
x = 25
Hence, angle a = 3(25) - 10 = 65°