Chain Rule Questions

The cost of printing a magazine of $540$ pages with $30$ lines on each page and $15$ words in each line is $\text{Rs. }7200$. Find the cost of printing a magazine of $450$ pages with $35$ lines on each page and $18$ words in each line.

A laboratory has to pay $\text{Rs. }67.50$ for $30$ days as a gas bill if it uses $35$ gas burners for $6\text{hours}$ a day. Find the amount to be paid if it uses $30$ gas burners for $18$ days working $7\text{hours}$ a day.