Answer: f= -11
Explanation: Know ur algebra lol
So, the area of the trapezoid is 287 cm².
So it is really easy to solve firstly we can see how much does the first 10 boxes make which makes around 75$ obviously. Secondly 55$ for the next 10 boxes.
So for now we can simply calculate that we have spent around 130$ which means 20 boxes. The remaining money left is 18$ so we can buy 18/4.5 = 4 only 4 boxes with that money. Hence a total of 24 boxes.
Yes D is the correct option !
if you want to know how , comment, or you are good to go !