Explanation:
remember, a square is a rectangle with 4 equal sides.
and the area of a square is (as for any rectangle)
length × width
and because length = width (and therefore simply just side) that means the area of the square is
side × side = side²
a.
in our case the area is
16x² ft² = side²
side = sqrt(16x²) = 4x ft
b.
the perimeter of a square is going along all 4 sides :
perimeter = 4 × 4x = 16x ft
c.
increasing the side by 5 ft means
side = 4x + 5
the perimeter is again going along all 4 sides :
perimeter = 4 × (4x + 5) = 16x + 20 ft
so, the new perimeter is 20 ft longer than the old perimeter.