Terri's project for the Math Fair is a magnificent black box that she called a function machine. If you put 3 into her machine, the output is 8. If you put in 10, the output is 29; and if you put in 20, the output is 59. Homework help

a. What would her machine do to an input of 5? What about -1? What about x?

b. Write an equation for Terri's machine​