Well 500+40x=700 is the equation with B, and with x=4 thats 500+160=700, which is NOT true. So, rosalina does not have enough money to purchase her new TV in 4 weeks.
Another Answer:
For the last one, I think that its referring to the A equation, but in any case it doesnt matter. Instead of adding 40x, you would be Subtracting 40x. I also can imagine what kind of job she has, only depositing 40 bucks a week. She spends too much money on video games and cheetos.
