Step-by-step explanation:
Start with 7y -1 + 9x+4 = 180 (straight line = 180° ) Solve for y
y = 25 2/7 - 9/7x
sub this in for 'y' in the sum of the triangle's angles
86 + 4x-7 + 7 ( 25 2/7 -9/7 x) - 1 = 180
compute this to find x = 15
then sub back in to the triangle sum:
86 + (4 (15) -7) + 7y-1 = 180
compute this to find y = 6
