Question 256438

x -3 -2 1 3 4 
f(x) 0  3 12 18 21 
As we see for each increase of x there is 3 increases of y.
The table can be extended:
x    -3 -2 -1  0 1  2  3  4
f(x)  0  3  6  9 12 15 18 21  
Then slope m=rise/run=3/1 and y intercept is 9.
Therefor equation is y=3x+9