Chemistry help-GCSE-atom economy

About 3000 tonnes of ibuprofen tablets are taken in the UK each year. Calculate the mass of waste created making 3000 tonnes of ibuprofen tablets at an atom economy of 40%.

Please could someone tell me the steps of working it out as I am finding it quite hard to work out

Thanks in advance

0.40 = mass of desired product/mass of reactants.

mass of reactants = (desired products)/(0.40)

3000 tonnes/.4 = 7500 tonnes

Reactants - desired products = waste

7500 - 3000 = 4500