A group of boys stood in three rows. The 1st row had 9d boys. The 2nd row had 7d fewer boys than the 1st row. The 3rd row had 4 more boys than the 2nd row.
- Find the number of boys in the 3rd row in terms of d. Give your answer in the simplest form.
- There were 20 boys in the 3rd row. Find the value of d.