Hello from MrBillDoesMath!
Answer:
35
Discussion:
There are 180 degrees in a line so 56 + y + 51 = 180 or
107 + y = 180 so y = 180 -107 = 73.
There are 180 degrees in a triangle so x + y + 72 = 180. But y = 73 (see above) so the equation is equivalent to x + 73 + 72 = 180 or x = 180 - 145 = 35, which is the first choice
Thank you,
MrB
