AB = length of the rope = L = 95 ft
AC = depth of water = h = 40 ft
BC = distance of the anchor from a point directly below the boat = x
consider triangle ABC
using Pythagorean theorem , we get
AB² = AC² + BC²
L² = h² + x²
inserting the values
(95)² = (40)² + x²
9025 = 1600 + x²
subtracting 1600 both side
9025 - 1600 = 1600 - 1600 + x²
x² = 7425
taking square root both side
x = sqrt(7425)
x = 86.2 ft