Audrey has less than 5 pounds of grapes. Here is where I think you made a typo. The question should indicate if Audrey has 5 pounds less of red grapes or green grapes.
Go back and check your original problem and then come back.
Since we know the ratio is going to stay constant at , we can use this to find the height of the lamp along with the information that the total distance from the lamp to the tip of his shadow is 20: