Step-by-step explanation:
Let y be the time required to cook the turkey, and x the number of pounds of the turkey.
The time required, x, is equal to the turkey's weight (in lbs) times 20 min/lb.
y = 20(min/lb)x
The domain of this function is 0 - 30 pounds.
The cook time for an 18 lb turkey is y = (20min/lb)*(18 lb) = 360 min
See the attached image.