5r=75
r=75/5=15
3f=75
f=75/3
f=25
4d=75
d=75/4
d=18.9
5r+3d+4f+75
The lowest must be ,,,,,when x=0
so
10y+30=0
10y=-30
y=-3
So your answer is (0, -3)
900 - 100 = 800
so the maximum weight allowable for passengers is 800lbs
I hope this helps! :)
~Ayden