Start with

Subtract 15 from both sides:

Divide both sides by 2a:

the graph at the bottom left hand corner is a function
Since Mr. Wilson has $3,000 and Ms. Nelson has 10 times more than that, we can set up a basic equation determining how much money Ms. Nelson has.

Ms. Nelson has $30,000 while Mr. Wilson has only $3,000.
C(12/15) because the other 3 all equal 0.666666666666667 but 12/15 equals 0.8