I think congruent angles are equal to each other. If not please stop here!
If they are congruent then:
(7x+15) = (2x+12)
7x+15-12 = 2x+12-12 [subtracting '12' on both sides]
7x+3 = 2x [solving above equation]
7x+3-7x = 2x-7x [subtracting '7x' on both sides]
3 = -5x [solving above equation]
\({3 \over -5}={-5x \over -5}\)[dividing by '-5']
\({-3 \over 5} = {x}\)[solving above equation]
There you go! :)
