To solve this, you would need to use the Pythagorean Theorem (a^2 + b^2 = c^2) In other words, one leg of the triangle to the power of two plus the other leg to the power of two is equal to the hypotenuse to the power of two.
The equation which would be made here is:
10^2 + x^2 = 26^2
10^2 is equal to 100, and 26^2 is equal to 676, so now we have:
100 + x^2 = 676
Now, we should subtract 100 from both sides:
x^2 = 576
Now, you find the square root of 576:
x = 24