Zöe schedules advertising for a radio station. She must fill 12 minutes each hour with 30 second ads and 60 second ads. Zöe sold twice as many 60 second ads as she did 30 second ads. She defines x as the number of 30 second ads and y as the number of 60 second ads that she sold. Zöe writes the system 2 x = y and 30 x + 60 y = 12. Which statement identifies Zöe’s error and the correction that is needed? a) Zöe used seconds to measure time for each ad, but she used minutes for the total. She should have used 0.5 x + y = 12.

b) Zöe set up an equation that would translate to “twice the number of 30 second ads = the number of 60 second ads.” She should have used x = 2 y.

c) Zöe compared the number of 30 second ads to the number of 60 second ads without including the total number of ads. She should have used 2 (30 x) + 1 (60 y) = 12.

d) Zöe did not include the whole hour in the total time. She should have used 30 x + 60 y = 60.