Hi there! To do this, we can divide both fractions. We have to convert the fractions into improper fractions. 15 3/4 (63/4) and 2 1/4 (9/4). To divide fractions, keep the first fraction the same, change division into multiplication, and flip the second fraction over. 63/4 * 4/9 is 252/36 or 7 when simplified. The average rate of speed was 7 miles per hour.