Well, 33.33% is usually seen in fraction form as 1/3, its one of those memory things (at least for me!).

So this becomes an easy problem once you see that part, you would then follow up by multiplying both fractions, so multiply the numerators (1 * 7 = 7) and the denominators (3 * 4 = 12) of each fraction together to get your new fraction

This would result in a new fraction of 7/12!

Hope this helped somewhat ^^