Answer:
15 hours to do the entire project
Explanation:
20% is the same as 1/5.
"percent" means "per 100", so 20% means 20/100 which reduces to 1/5.
20% of an art project took 3 hours. That means that 1/5 of the art project took 3 hours. The entire project then takes 5 times as much time.
5 * 3 hours = 15 hours
It takes 15 hours to do the entire project.
15 - 3 = 12
It takes 12 more hours after 20% was done.