Question

The graph shows the relationship between the total amount of money that Carly will have left, y, if she buys x packs of baseball cards.

A graph titled Money Left after Purchase. The x-axis shows packs of cards bought, numbered 1 to 9, and the y-axis shows the money left (in dollars), numbered 2 to 18. Blue diamonds appear at points (1, 16), (2, 12), (3, 8), (4, 4), (5, 0).
How much money will she have if she doesn't buy any packs of baseball cards?

Answer 1

choices pls

Answer 2

because x represents the # of card packs bought, we want to find out the value of y when x = 0. or in other words, the y-intercept.

to do that, take any two points
ex: (4, 4), (5, 0) will make the arithmetic easier
calculate the slope

then plug in the m-value, along with any point (x,y) into the equation y = mx + b and solve for b. this b-value is the y-intercept, and thus the amount of money left at 0 baseball packs.

alternative method: if 1 pack leaves her with $16, and 2 packs leaves her with $12, then naturally 1 pack costs 16 - 12 = $4

if 5 packs, at $4 each, leaves her with $0, how much money did she have to begin with?