Let l be the length

w be the width

A be the area

As it states, the length is 4 times the width so we can write this as 4w. Next, we need to know the formula for the area of a rectangle. The formulas is this:

A = l × w

Next, we simply SUBSTITUTE the value for l into the formula to find the area and that will allow us to solve for w. We know that the area is 80cm so we can just write that,

80 = (4w)(w)

Now let’s solve for w.

Step 1: Simplify both sides of the equation.

80=4w^2

Step 2: Subtract 4w^2 from both sides.

80−4w^2=4w^2−4w^2

−4w^2+80=0

Step 3: Subtract 80 from both sides.

−4w^2+80−80=0−80

−4w^2=−80

Step 4ivide both sides by -4.

−4w^2/−4=−80/−4

w^2=20

Step 5: Take square root.

w=√20

w = ~4.5 (rounded to tenth)

now that we know w we can solve for l.

remember. l = 4w

l = 4(4.5)

l = 18

we can check this by calculating the area where l is 18 and w is 4.5.

A = l × w

A = 18 × 4.5

A = 81 ( should be 80 but we rounded)