We have the following right triangle:
And we need to find the measure of the side represented by x.
To find it, we can proceed as follows:
1. Apply the Pythagorean Theorem as follows:

We have that the sum of the squares of the legs (5 in and x inches) of the right triangle is equal to the square of the hypotenuse (10 in).
2. Then subtract (5in)^2 from both sides of the equation:

3. Now, we can extract the square root to both sides of the equation (without using units):

4. Finally, to simplify the number at the right of the equation, we can factor the radicand as follows:
And these are the prime factors for 75. Then we can rewrite the value as follows:

Therefore, in summary, the value for x is:

[Option B.]