F(5)=-1 and f(6)=2

Answer 1

The two sets of coordinates are (5,-1) and (6,2) --- x is input to function; y is output of function

compute slope (2--1)/(6-5) = 3

select one of two coordinates, say (6,2)

y - 2 = 3(x-6)

y = 3x - 18 - 2

y = 3x - 20