Explanation

To find how many shirts the washerman can iron in one hour (60 minutes), we can use the given rate:

• The washerman irons 4 shirts in 12 minutes.

Now, let's find how many sets of 12 minutes are there in 60 minutes:

60​/12=5

Since he can iron 4 shirts in 12 minutes, in 60 minutes he can iron:

4×5=20 shirts