Question: how to subtract larger fraction from smaller fraction?
Answer: Write both fractions as equivalent fractions with a denominator of 15. Since you're trying to subtract a larger fraction from a smaller one, you need to "borrow" a one from the integer 4, change it to 15/15, and add it to the fraction. Now the problem becomes 3 20/15 minus 3 9/15 and the answer is 11/15.