Explanation:
an object and its shadow create a right-angled triangle.
2 objects and their shadows at the same time create therefore two similar right-angled triangular
triangles.
that means the angles are the same, and each side length of one triangle correlates to the corresponding side length of the other triangle by the same factor.
so, when we know the factor of one pair of sides, we can calculate the lengths of the others by using the same factor.
therefore,
1.57 × f = 50.5
f = 50.5 / 1.57 = 32.1656051...
the height of the tower is then
3.1 × f = 3.1 × 32.1656051... = 99.7133758... m ≈ 100 m