Tickets for a school jazz concert were sold before the concert and at the door. After reviewing ticket sales, the band director found that 80 fewer tickets were purchased at the door than before the concert. A total of 520 tickets were sold. Let d represent the number of tickets sold at the door and b represent the number of tickets sold before the concert. Latifa wrote the following system of linear equations to find the number of each type of ticket sold: d plus b is equal to 520 d minus 80 is equal to b What is Latifa’s error?