Answer:
the volumes they would have read is 20
so it will take them 5 weeks
Step-by-step explanation:
C ( started with 10) < 12<14<16<18<20 =5 weeks
L (started with 0) <4 <8<12<16<20 = 5 weeks
for them to read the same book will take them 5 weeks and each of them would have read 20 volumes by then