Since her base amount is 1200, we have 1200+<number>=<number>. Since she gets 35 dollars for every phone, if the number of phones she sells is x, we have 1200+35*x=the total amount of money in a month =4000 . Subtracting 1200 from both sides, we get 2800=35*x and by dividing both sides by 35 we get x=80
