I cannot see Zoe's work to explain the error, but the correct method of solving is listed:
x is the number of 30-second ads
y is the number of 60-second ads
x+y=12(60)=720 would be the first equation; this is because while the ads together make 12 minutes, the ad times are in seconds. This means we must multiply 12 by 60.
y=2x is the second equation
Our system is then
x+y=720
y=2x
We will use substitution to solve this. Plug 2x in place of y in the first equation:
x+2x = 720
Combine like terms:
3x = 720
Divide both sides by 3:
3x/3 = 720/3
x = 240
Substitute this value in for x in the second equation:
y=2(240)
y=480
Substitute 4y for x.
2(4y)-3y=-15
8y-3y=-15
5y=-15
Dividing by 5, we see that y=-3.
The first 5 multiples of 3 are 3, 6, 9, 12, and 15.
Answer:
D
Step-by-step explanation:
