Plzz help I need #16 and #18

In #16, every time 'x' increases by 1, the function increases by 3.
So you know that the slope is 3.
But the function isn't simply 3 times x .  It's 4 less than that.

f(x) = 3x - 4

In #18, every time 'x' increases by 3, the function increases by 15.
So you know that the slope is 15/3 = 5.
But the function isn't simply 5 times x .  It's 2 less than that.

f(x) = 5x - 2