We can help you and somebody can help you with calculator
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.