How do i know if it's a function or not?

Need santino bought a 3/4 pound bag of chocolate chips. he used 2/3 of the bag whule baking. how many pounds of chocolate chips did he use while baking?

Ashopper bought a watermelon a pack of napkins and some paper plates in his state there was no tax on food the tax rate on non-food items is 5% the total for the three items he bought was 825 before tags and he paid $0.19 in taxes how much did the watermelon cost

If f(x)= 3x+6 which of the following is the inverse of f(x)