Answer:
The minimum cost would be 480$ when Inna works for 8 hours and Jim works for 20 hours.
Step-by-step explanation:
We are given the following information in the question:
Charges for 1 hour for Inna = $15
Number of pages typed by Inna in 1 hour = 6
Charges for 1 hour for Jim = $18
Number of pages typed by Jim in 1 hour = 8
Let x be the number of hours Inna work and let y be the number of hours Jim work.
Total cost = 
We have to minimize this cost.
Then, we can write the following inequalities:

The corner points as evaluated from graph are: (8,20) and (24,8)
C(8,20) = 480$
C(24,8) = 504$
Hence, the minimum cost would be 480$ when Inna works for 8 hours and Jim works for 20 hours.
The attached image shows the graph.