A glass of water is $\dfrac{3}{7}$ full and $\dfrac{4}{7}$ empty. It has 6 ounces of water in it. How many ounces of water can the glass hold?

If the glass holds x ounces of water and if it is 3/4s full, then (3/4)·x = 6

Multiply both sides by 4: 3x = 24.

Divide both sides by 3: x = 8.