Answer:
x = 3
Explanation:
An equilateral ∆ has equal side lengths and all its angles are also equal to each other, which are 60° each.
The ∆ given has equal side lengths. Therefore it is an equilateral ∆ having equal angles, each would measure 60°.
Thus:
(25x - 15) = 60°
Solve for x
25x - 15 = 60
Add 16 to both sides
25x - 15 + 15 = 60 + 15
25x = 75
Divide both sides by 25
25x/25 = 75/25
x = 3