Joe is buying school supplies. He buys 2 pencils, 4 erasers, 10 pens, and a backpack for $20. Pencils and pens cost the same amount. If ​p​ represents how much each pencil and pen costs, and ​e ​represents how much each eraser costs, the following expression shows how much Joe spent on school supplies:
2p + 4e + 10p + 20
a)​ ​Simplify Joe’s total spending expression.
​Simplified Expression: _______________________