Answer:
b) 20 minutes
Step-by-step explanation:
Tom=0.5Mike
in 15 minutes, Tom will have done 1/2 of the lawn
in 15 minutes, Mike will have done 1/4 of the lawn
in 15 minutes, they will have done 3/4 of the lawn
15/3=5 minutes for 1/4 of the lawn to be done
5x4=20 minutes for the entire lawn