I must calculate how much money I'll spend next week. ✬

How do you calculate the length of the circumference? I've forgotten. ✬

How do you calculate the volume of a cube? ✬

Tom couldn't calculate the price of the collection. ✬

I can't calculate the distance. ✬

It's not hard to calculate. ✬

The bill was hard to calculate. ✬

The bill was difficult to calculate. ✬

It isn't hard to calculate. ✬

It isn't difficult to calculate. ✬