Using the numbers you have :
6 to -2
-2 to 2
4 to 1
-1 to 1
This is a function.
An input can only have one output, but an output can have multiple inputs.
Well draw a box with 10 squares going up and 20 square is going sideways and then shade and 5/8 of it
400 / 10 = 40.
40
X 9
= 360
In a group of 400 smokers, about 360 of them started before they reached their 21st birthday.