Please help, can u explain if you know, thanks a lot

This means that you are finding the length, since length X width = area. if we know that the area is 36ft^2 and the width of 4 feet, you will divide the area by the width to find the length.

for example:
36 divided by 4...
= 9

9ft^2 is the length of the rectangle. you can check your answer too, by multiplying the known width by the length that we just found.

4x9=36, therefore the length of the rectangle is in fact 9.

D