If you have to get the length of a rectangle, given its width and area, you will still use the standard formula: A = length x width. You just have to substitute the given to the formula.
Example:
A= 60 w=5
FInd its length:
A = L x W
60 = L x 5
60 = 5L
60/5 = 5L/5
15 = L
There you go :)
