how would i graph this? i understand how i would graph the (x-1)^3 but the f(x)-3 part confuses me lol

First you want to know the profits of the three ppl. so: 
4800/3=1600
then u make an equation with proportions: 9x+7y+4x=4800
add the invests: 9+7+4=20x and 4800 would stay same. 
then divide 20 by 4800 to get 240 
now plug the investments to 240 
9 times 240 is 2160 
7 times 240 1680 
4 times 240 is 960
last you must subtract to find x as the investments 
take 1600 and subtract it by 2160 and you get x=560 
$560 is your answer 
hope i helped :D