Explanation

To determine how many shirts a person can iron in one hour, given that they iron four shirts in 12 minutes, follow these steps:

1: Calculate the time to iron one shirt:

12 minutes for 4 shirts means 1 shirt takes 

12/ 4 =3 minutes.

2: Determine how many shirts can be ironed in one hour:

One hour = 60 minutes.

If one shirt takes 3 minutes, then in 60 minutes, the number of shirts ironed is 

60/ 3 =20 shirts.