Well you start of in reverse. The formula to find the Area of a parallelogram is A = bh so since you already have the Area all you would have to do is divide the area by the height like so 26 1/2 / 6 5/8 = 4. So to make sure you have the right answer you would just Multiply 4 by 6 5/8 to see if it equals 26 1/2.
4 X 6 5/8 = 26 1/2
I hope this helped