Answer:
If using A, B, C, as variables for the measure of the corresponding interior angles, and A is the vertex point, B and C are the base angles, triangle isosceles, then:
system%28A=4y%2B10%2CB=75%2CC=3x%29
Angle mesures at B and C are equal (base angles of isosceles triangle).
B=C
75=3x
highlight%28x=25%29