This is just a triangle on top of a rectangle.
A=hb/2+xy, In this case:
A=7.2*25/2+25*12.9
A=413.125
The the force equation becomes:
F=.004Av^2 we want to know what this force is when v=81, together with the area found above you have:
F=.004(413.125)81^2
F=10842.0525 pounds.
Each ton is 2000 pounds so
10842.0525/2000≈5.4 tons
which is just 5 tons to the nearest whole ton...
