Answer:
She must pay $500 for the materials, and $14 per lawn, then:
We know that the total cost is (assuming that they work for 8 weeks, 6 days per week, and 3 times per day)
C = $500 + $14*(8*6*3) = $2,516.
The total revenue that she can make (with the same assumptions as before) is:
R = N*(8*6*3)
Where N is the amount she charges for each lawn that they mowed.
R = N*144
Now, we do not know how much she charges, so the value of N is unknown.
Now, the profit is equal to the difference between the revenue and the cost, this means that the profit is:
P = R - C = N*144 - ($2,516)
P(N) = N*144 - ($2,516)
If we have, for example, N = $20, the total profit will be:
P($20) = $20*144 - ($2,516) = $364
