10x = 15y + 5 (by the vertical angle theorem). 8x + 1 + 7y + 10x = 180 ( by triangle sum theorem) 18x + 7y = 179 .............(1) from first equation :- 10x - 15y = 5.................(2)
Multiply (1) by 10 and (2) by -18:- 180x + 70y = 1790 -180x + 270y = -90 Adding :- 340y = 1700 y = 5 and from first equation 10x = 15(5) + 5 = 80 x = 8
