Question

I have he a question on this one equation that someone sovled.

An isosceles triangle in which angles B and C have the same measure. Find the measure of each angle whose degree is represented with variables.
A= 4x + 2y
B= 9y - 2
C= 10x + 10

We know B = C,so we know 10x + 10 = 9y - 2
thus x = (9y -12)/10
and A + B + C = 180
14x + 11y + 8 = 180
14 (9y - 12)/10 + 11y = 172
126y - 168 + 110y = 1720
236y = 1888
y = 8
x = (72 - 12)/10 = 6
So B = 70
C = 70
A = 40

On Equation
x = (9y -12)/10 how did someone get 14 on this equation: 14 (9y - 12)/10 + 11y = 172

Answer 1

14x + 11y + 8 = 180

Replace x above by (9y -12)/10 from the equation "thus x = (9y -12)/10" three lines back.
14 (9 y - 12)/10 + 11 y = 172
Multiply each side by 10
14 (9 y - 12) + 110 y =1720
Expand the left side.
-168 + 236 y = 1720
Move -168 to the RHS
236 y=1720+168
236 y=1888
y=8

Answer 2

Attached is a two step Mathematica solution.