Amachinist can produce 12 parts in 40 min.how many parts can the machinist produce in 4 hours?

72 parts

Steps:

Convert the 4 hours into minutes. There are 60 minutes in an hour. Therefore, 4 hours = 240 minutes.

Divide 240 minutes by 40 minutes. This equals 6. Therefore, the machinist can produce the 12 parts 6 times in 4 hours.

Finally, multiply the 12 parts by the 6 times he can produce. Therefore, the machinist can produce 72 parts in 4 hours.

The correct answer is b