I'm trying to solve this: A firm has seen its demand doubled over a 2 year period. During the same period, the flow time has reduced by 30%. What has...

I'm trying to solve this:

A firm has seen its demand doubled over a 2 year period. During the same period, the flow time has reduced by 30%. What has happened to inventory over the same period? (use Little's Law)

I know the formula is Inventory = Throughput Rate x Flow Time. But I'm not sure how to get find throughput rate with just knowing demand.