The right triangle formed by the flagpole and its shadow is shown below
From the right triangle,
BC represents the height of the flagpole
AC is the hypotenuse of the triangle
AB is the length of the shadow
To find BC, we would apply the pythagorean theorem which is expressed as
hypotenuse^2 = one leg^2 + other leg^2
one leg = BC
other leg = 48
By applying the theorem, we have
52^2 = 48^2 + BC^2
2704 = 2304 + BC^2
Subtracting 2304 from both sides of the equation, we have
2704 - 2304 = 2304 - 2304 + BC^2
BC^2 = 400
BC = square root of 400
BC = 20
Option D is correct