A dairy supplies 2520 litres of milk in 7 hours.

(a) Calculate the milk supplied per hour \(=\) litres.

(b) Determine the supply in 3 hours \(=\)   litres.

(c) Determine the supply in 13 hours \(=\)  litres.

(d) Find the time required to supply 6120 litres \(=\) hours.