since its an isosceles triangle, which is divided at the centre,
the remaining length of the given right angle triangle is 5
using pythagoras theorem to find x
x^2 = 8^2 - 5^2
x^2 = 64 - 25
x^2 = 39
x = square root of 39
x = 6.25
therfore the answer is:
A. 6.25