Solve the equation by using the quadratic formula.
The distribution of income in a certain city can be described by the mathematical model $y=\left(5.6 \cdot 10^{11}\right)(x)^{-1.5},$ where $y$ is the number of families with an income of
$x$ or more dollars.
a. How many families in this city have an income of 30,000 dollar or more?
b. How many families have an income of 60,000 dollar or more?
c. How many families have an income of 150,000 dollar or more?