Manoj can complete a work in 15 days working 8 hours in a day and Santosh can complete it in 10 days working 9 hours in a day. If Manoj and Santosh together start working for 6 hours per day, in how many days will they complete the work?

A

12

B

$$8\frac{4}{7}$$

C

$$10\frac{4}{7}$$

D

7