Shane & Sons Watchmakers Has Many Departments

Shane & Sons Watchmakers has many departments.Of these,Department A occupies 20 square metres of floor space while department B occupies 30 square metres.If rent for the whole factory totals $1000 per week and the total floor space taken up by the factory is 200 square metres,how much in rental costs must be allocated to Department B?

A) $150
B) $100
C) $400
D) $600