Answer:
The expression is : 
Step-by-step explanation:
Every week for 20 weeks, Kathy earned $15 for mowing lawns and $35 for delivering newspapers.
In 20 weeks, the earnings from mowing lawns will be = 
In 20 weeks, the earnings from delivering newspaper will be =
At the end of 20 weeks she spent $300 and was left with :
dollars
Or can be written as :
dollars
This is the expression to solve the problem.