Two triangles are similar if their corresponding sides have an equal ratio
Since the sides of the 1st triangle are x, x, and 50
Since the sides of the 2nd triangle are 45, 45, and 75
Since the two triangles are similar by the SSS theorem, then
By using the cross-multiplication between the 1st or 2nd ratio and the 3rd ratio
Divide both sides by 75
The value of x is 30