Answer: Sara bought billboards with 4 lines for $20 (the quantity is 7)
We have to take the total cost (t) and divide that buy the 6 lines billboards and the 4 line billboards.
- We know one 6 line billboard = $30
- We know one 4 line billboard = $20
So, let's divide $140 by 20 and 30 (the cost for each type of billboard).
$140 ÷ 30 = 4.6
This can not be the answer because Sara bought 7 billboards, not 4.6
$140 ÷ 20 = 7
So, the answer is Sara bought billboards with 4 lines for $20.
Hope this helps you!