Inverse function: you need to exchange the position of x and y, in other words,
x = (5-2y^2)/(3y+10) , then, if you need a representation of y with respect to x, then you need to perform some math.
If you would like to know what is the unit price for the hair shampoo, you can calculate this using the following steps:
500 ml ... $2.10
100 ml ...$x = ?
500 * x = 2.10 * 100 /500
x = 2.10 * 100 / 500
x = $0.42
The unit price for the hair shampoo is $0.42.
Tape diagrams are simple. Look at the picture I put in the comments