8
1) Let's sketch that to better understand it
2) In this case, we can solve it using the Pythagorean Theorem. So
a²=b²+c² Hypotenuse squared is equal to the sum of those legs squared.
Plugging into that
10²=b²+6²
100=b²+36 Subtract 36 from both sides
100-36=b²
b² =64 Take the square root on both sides
√b² =√64
b=8 The negative value -8 is ignored since dimensions can't be negative.
3) Hence the answer is 8