The shown triangle is an isosceles triangle.
Note: An isosceles triangle has equal angles corresponding to the equal sides.
We are given an angle 25 degrees.
Another angle on right side corresponding to the equal side is also equal to 25 degrees.
Sum of all three angles of a triangle is 180 degrees.
Therefore, 25 + 25 + top angle (x+x) = 180 degrees.
Therefore,
on adding 25+25 we get 50 and x+x=2x.
We get 50 +2x = 180.
Subtracting 50 from both sides, we get
50-50 +2x = 180-50
2x = 130.
Dividing both sides by 2, we get
x = 65.
Therefore, unknow angle x= 65 degrees.