Answer:
A
Explanation:
the height a creates with half of the baseline (5) and a leg (10) a right-angled triangle, and we can use Pythagoras to calculate a.
c² = a² + b²
c being the Hypotenuse (the side opposite of the 90° angle, so in our case the 10 side).
10² = a² + 5²
100 = a² + 25
75 = a²
a = sqrt(75) = sqrt(3×25) = 5×sqrt(3)