Answer:
(a)
(b)
Step-by-step explanation:
Alphaville's Budget Surplus Model is 
Betaville's Budget Surplus Model is 
We want to determine the expression that shows how much greater Alphaville’s annual budget surplus is than Betaville’s for a particular amount of tax revenue.
- To do this, we subtract Betaville's Model from Alphaville's model.

Opening the brackets

Collect like terms and simplify

The expression that shows how much greater Alphaville's Budget is:

(b) If the tax revenue that year in each town is $75,000
We want to evaluate the expression derived above when the tax revenue that year in each town is $75,000 i.e.at x=75000
