Answer:
9
Step-by-step explanation:
Okay, we know that 6=2/3 of the cost.
that means that 3 is 1/3 of the cost.
It looks like you mistook 2/3 for 1/3 and multiplied 6 or something but this is fairly simple.
On top of 6 you are going to add 3 so you get the full cost because 2/3+1/3=3/3
You get 9
