we know from the markings on the sides of the triangle that this is an equilateral triangle. The angles of an equilateral triangle are all equal. because of this, we can put these two equations to equal each other
since we are solving for y, we want to isolate y on one side.
6x+6=5y+10
-10 -10
6x-4=5y
divide both sides by 5
6/5x-4/5=y