Plz plz help i have till 11 50 plzplz plz help

You are on a cycling trip around europe with friends. you check the weather forecast for the first week. these are the temperatures for the week. sun mon tues wed thurs fri sat 16°c 20°c 24°c 28°c 28°c 23°c 15°c what is the mean temperature forecast for the week?

Ineed with math stuff it involves graphs

Solve the formula ax+ by = c for x.