Standard and express parcels

A warehouse dispatches \(150\) parcels. Standard parcels weigh \(2\) kg each and express parcels weigh \(3.5\) kg each. Their total mass is \(375\) kg. Let \(s\) be the number of standard parcels and \(e\) be the number of express parcels.

1. Form two equations in \(s\) and \(e\).
2. Solve the equations obtained in (a) to find the number of parcels of each type.
3. A standard parcel costs \(\$4\) to send and an express parcel costs \(\$7\) to send. Hence, find the total delivery charge.