1. To solve this problem, you must use the formula of the area of a rectangle, which is shown below:
A=lxw
"A" is the area of the rectangle (A=5400 cm²).
"l" is the lenght of the rectangle (l=2w-30).
"w" is the width of the rectangle.
2. When you substitute l=2w-30 into the formula A=lxw, you have:
A=lxw
5400=(2w-30)(w)
5400=2w²-30w
2w²-30w-5400=0
3. Now you have a quadratic equation. When you solve it, you obtain the value of "w". Then:
w=60 cm