The value of x = 52.
The triangle image you sent shows a right triangle with a hypotenuse of 5x+15 degrees and one leg of x degrees. We can use the Pythagorean Theorem to find the other leg, y degrees:

Since the triangle is a right triangle, we know that y = 90 - x. Substituting this into the equation above, we get:

Expanding the parentheses on the right-hand side of the equation, we get:

Combining like terms and simplifying, we get:

x = 52