Mia and the Breakfast Diner

Mia is working as a waitress at a breakfast diner. She can take up only one shift from 6 shifts a day i.e. from 10 am to 4 pm. She needs to save 300\$ after completion of the month. She works only for $D$ days in the month. She estimates that she gets her highest tip in the first shift and the tip starts decreasing by 2% every hour as the day prolongs. She gets a minimum wage of $X$ \$ for every s