Use X and Y to create a function and describe how its a function.

Y=mx+b

f (x) = 3x+4

This is a function because it shows that the y value is equivalent to 3 times the x value plus 4. the 4 is used to represent the y intercept, which is were the function's line intercepts the y axis (it intercepts at 4 units). For ever value of x, f (x) is four more than three times x.