Camille bought 120 donuts for $60. Her profit was $48 once she sold 80 donuts. Write an equation that represents Camille's profit (P), as a function of the number of donuts sold (n)?

We have been given two pairs of (n, P). They are (n, P) = (0, -60) and (n, P) = (80, 48). Using these, we can write the function as a linear equation in two-point form.
  P-48 = (n-80)/(0-80)*(-60-48)
  P = (108/80)(n-80) + 48
  P = 1.35n - 60