Answer: x=3
Need to knows: Triangles have 3 angles add up to 180 degrees. This specific triangle is an equilateral based off of it's markings.
First, divide 180 by 3 because there are 3 angles that are equivalent and you will get 60.
Second, therefore the equation you should set up, and plan to solve would be: 25x-15=60
Third, add 15 to both sides of the equal signs. The -15 will cancel out on the left side and then on the right side of equal sign you should have added 15 to 60 and that equals 75.
Fourth, you will be left with 25x=75. So you will have to divide 25 on both sides and you're answer will be x=3.