Answer:
1.71 min per pizza
Step-by-step explanation:
Ren's rate:
3 min per pizza (take inverse to get pizza per min)
= 1/3 pizza per min
Issac's rate:
4 min per pizza (take inverse to get pizza per min)
= 1/4 pizza per min
Combined rate = Ren's rate + Issac's rate
= 1/3 + 1/4
= 4/12 + 3/12
= 7/12 pizza per min (take inverse to get min per pizza)
= 1 / (7/12) min per pizza
= 12/7 min per pizza
= 1.71 min per pizza