Problem solving Q about making bottles in a factory

Question

A company orders a number of bottles from a factory.

The 8 machines in the factory could make all the bottles in 5 days. All the machines work at the same rate.

For 2 days only 4 machines are used to make the bottles. From the 3rd day all 8 machines are used to make the bottles.

Work out the total number of days take to make all the bottles.

I don't know how to approach this question. Thank You and help is appreciated

Answer 1

Hint:

You need $8\times 5=40$ "machine-days" for making the bottles.

In $n\geq2$ days there are $4\times2+8\times(n-2)$ machine-days.