What is the perimeter of a rectangle if ti's area is 15ft?

Answer 1

The area cannot be 15 feet since that is a measure of length, not area.

In any case, information about the area cannot determine the perimeter; it can only put a lower limit on it. The perimeter can be anyhting from 15.49193 ft upwards.

Consider the following rectangles, all with area = 15 square feet:

a sqrt(15)*sqrt(15) rectangle will have a perimeter of 4*sqrt(15) = 15.49193 ft (approx).

1ft*15ft rectangle will have a perimeter of 32 feet

0.1ft*150ft rectangle: perimeter = 300.2 feet

0.01ft*1500ft rectangle: perimeter = 3000.02 ft

0.001ft*15000ft rectangle: perimeter = 30000.002 ft

by now you should see that there is no upper limit to the perimeter.