9th grade
posted by Amy .
it cost $2 per day to place a oneline ad in the classifieds plus a flat service fee. one day cost $3 and four days cost $9.
write a linear equation that gives the cost in dollers, y, in terms of the nunber iof days,x.
find the cost of a sixday ad.

Actually you have more information than is necessary.
"it cost $2 per day to place a oneline ad in the classifieds plus a flat service fee" > y = 2x + b
"one day cost $3 " > x = 1, y = 3
3 = 2(1) + b
b = 1
equation: y = 2x + 1
(check: 4 days cost $9,
y = 2(4) + 1 = 9, Check!
so for 6 days
y = 2(6) + 1 = $13