Answer:please refer to the explanation section
Step-by-step explanation:
Mechanic = $100
Vet = $100
Alex (payment from vet) = $100
Will's $100 bill has created $300.
This situation is explained in detail by the concept known has the multiplier. The multiplier measures how much impact will a change in an exogenous variable will cause in endogenous variables, for example How much a increase in Government spending will change Gross Domestic Product.
The multiplier in this case is 3,