CONCEPT: Time and Work

-Calculate unit work to breakdown data for 1hr or 1 day.

SOLUTION:

Work of A in one hour=1/10

B+C in 1 hour=1/4

A+B+C=(1/10+1/4) in 1 hour=14/40 products

Given, total number of products they completed working together=14

Hence total time to complete= 14/(14/40)=40 hrs.(C)