Answer :
We have 2 unknowns, therefore we have to set up two equations as well. The equations would be as follows:
180 = angle A + angle B + angle C
180 = x+8y-1 + 3y+4 + 7x+5 -----------> Equation 1
8x + 11y = 172
B = C
3y+4 = 7x+5 --------------> Equation 2
3y -7x = 1
x = 5
y = 12
Angle A: 100
Angle B: 40
Angle C:40
180 = angle A + angle B + angle C
180 = x+8y-1 + 3y+4 + 7x+5 -----------> Equation 1
8x + 11y = 172
B = C
3y+4 = 7x+5 --------------> Equation 2
3y -7x = 1
x = 5
y = 12
Angle A: 100
Angle B: 40
Angle C:40