30% of number A means
similarly, 40% of number B means
These must be equal, so we have
Multiply both sides by 10 to get
So, you can choose any number for A, and then you multiply it by 4/3 to get B. There are infinitely many solutions to this equation.
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.