Input Output
2 8
9 36
? 16
7 28
Have the child pretend he is an Archer. Explain to them that every arrow they shoot will get them four points if it hits the Bull Eyes.
Show them that if 2 arrows hit it, this yields 8 points. If 9 hit it they get 36 points etc.
Then have them figure out how many arrows it would take to get 16 points.
A visual might help. Like a big Bulls Eye, and arrows with the number 4 on them.