It's a straight angle which = 180 degrees.
( -7x + 12 ) + ( -8x + 48 ) = 180
combine like terms
-7x - 8x + 12 + 48 = 180
-15x + 60 = 180
-60 -60
15x = 120
(divide by -15 on both sides)
x = -8
substitute for "x" in the expression ( -7x + 12 )
After simplifying your expression youbsgiukd end up with 68 degrees for your answer.