This is an equilateral triangle, a triangle that has 3 congruent/equal sides and 3 congruent angles.
A triangle is 180°, so the three angles should add up to 180°.
Since you know this triangle has 3 equal angles, each angle should be 60°
(60° + 60° + 60° = 180°)
To find x, you can do:
(25x - 15) = 60 (because you know each angle is 60°)
To isolate x, you can first add 15 on both sides
25x - 15 + 15 = 60 + 15
25x = 75 Divide 25 on both sides
x = 3
