I don't know if you meant profit or markup but,
take the difference of $80 & $50 = $30
What percent of 50 is 30? It's 3/5 or 60%. So there is a 60% markup on the original price of 50$.
2÷5=0.4
1÷4=0.25
0.4÷0.25=0.016
so she walks at a rate of 0.016 miles per hour
From multiplying the binomial expression
(n+3)(n-9)
It would be n^2 - 9n + 3n - 27 or simplified
n^2 -6n - 27.