Height usually refers to three dimensional objects, so I assume you mean height.
The formula for area is:
Area = length • width
If you were given the width and area of the rectangle you would be able to find the length by doing inverse operations. In this case, the opposite of multipication is division
Example: 56 = l • 8
56 / 8 = 7
56 = 7 • 8
The length is 7.
I hope this helps!