Help please how do I solve for k

In a box lenght 1m breadth 60 cm and height 40 cm small rectangular packets of dimension 5 cm into 8 cm into 10 cm are packed. how many such small packets can be packed in the big box?

You are a clerk at convenience store. a customer owes 11.69 for a bag of potatoes chips. she gives you a five dollar bill. how much change should the customer receive?

Define multiplicative inverse. give an example of a number and its multiplicative inverse.