The sum of 3 times a number and 1 is 17 decreased by the number

An architect is designing a water fountain for a park she uses the given function to model the water jet flowing from the fountain nozzles where h(x) gives the height of the water jugs in feet x feet from the starting point h(x)=-1/20x+x+15

If 10 men take 18 days to mow 60 acres of grass, how long will 15 men take to mow 80 acres?

How do you solving the solution of each system using elimination?