Based on this information, what is the cost, in dollars, of one pack of markers?

Let m be the cost in dollars of one pack of markers and e be the cost in dollars of one large eraser. Based on the information given, we can create a system of two linear equations.

First purchase: m + 2e = 7

Second purchase: m + 4e = 9

To find the cost of one pack of markers, m, we can solve this system. One way is to subtract the first equation from the second equation:

(m + 4e) - (m + 2e) = 9 - 7

m + 4e - m - 2e = 2

2e = 2

e = 1

This tells us that the cost of one eraser is $1. The question asks for the cost of one pack of markers, m. We can substitute the value of e into the first equation:

m + 2(1) = 7

m + 2 = 7

m = 5

Therefore, the cost of one pack of markers is $5.

A is incorrect. This is the cost of one eraser, e, not one pack of markers, m.

B is incorrect. This is the difference in the total costs ($9 - $7 = $2), which corresponds to the cost of two erasers, not one pack of markers.

D is incorrect. This is the average of the two purchase totals (($7 + $9) / 2 = $8). This value does not represent the cost of a single item in this context.