Answer :
Step-by-step explanation:
Old Railroad Car:
- 1 day of coal in 15 hours
- 1/15 days of coal in 1 hour
New Railroad Car:
- 1 day of coal in 10 hours
- 1/10 days of coal in 1 hour
Total number of days of coal in 1 hour
= 1/15 + 1/10 = 1/6.
Since there is 1/6 days of coal in 1 hour,
there will be 1 day of coal in 6 hours.
It will take them 6 hours to transport the supply.