Answer:
First of all, let's multiply both sides by 5, clearing the denominators:
Then, as long as g is not zero, we can divide by g, and let's read right to left:
At this point, assuming F and g are either both positive or both negative, we can take the square root of both sides:
If h represent a quantity that is positive by it's nature (ie, the length of a segment) you can consider only the positive root, ie ignoring the plus or minus sign.