Kindly explain what was being taught here please. I have a hard time understanding it

Real life application of functions Problem 1 1. A rectangle has a perimeter of 60 ft.. Express its area A as a function of the length x. 60 - 2x GIVEN: SOLUTION: WE 2 Let length (x) = 20 ft. P = 2(length) + 2(width) 60 2x W= Let x = length 2 For Area N W = 30 - X A = (30 ft) (20 ft) - (20 ft)2 Let w = width For Area A = 600 ft2 - 400 ft2 A = 200 ft2 A = Area A = (length)(width) For Width P = 2x + 2w = 60 A = x (30 - x) W = 30 ft - 20 ft W = 10 ft Solve for w in terms of x Express the area as a function of x Check if P = 60 ft. 2x + 2w = 60 A(x) = x (30 - x ) P = 2(length) + 2(width) 2w = 60 - 2x A(x) = 30x - x2 P = 2(20 ft.) + 2(10 ft) 2w 60 - 2x P = 40 ft. + 20 ft. P = 60 ft. 2 2