For a linear function, you want it in y= mx + b form
They give you the slope your x, and when they say f(7)=1 that's like saying when x=7, y=1, or the ordered pair (7,1). To make it in y=mx+b, you can plug these coordinates in to solve for b. So, 1=7(7)+b, after you plug in slope and your point. Do math, 1=49+b, b=-48
That's how I think it's done