I belive its D dont take my word for it but i belive that is the answer
Since the photo booth charges a $500 fee for two hours at the party and an additional 50 dollars per hour, we have:
50x+500=C
Where x is the hours stayed and C is the total cost. Since Cindy doesn't want to spend more than 700 dollars, we have:

So she spent an additional 4 hours on the rental.
She earns $825 more as a head buyer than a assistant buyer
Given the proportion 7/5=x/3, you can cross-multiply to find the value of x.
21=5x.
Divide both sides by 5.
x=4.2.
Hope this helps!