Answer:
On day 5, he should be able to do 11
Step-by-step explanation:
Day 1 - 3
Day 2 - 5 (2 more than day before)
Day 3 - 7 (2 more than day before)
Day 4 - 9 (2 more than day before)
Following this pattern of +2, day 5 should be 11.
that's my thought process, so I hope it works