A hardware store sells light bulbs in different quantities. the graph shows the cost of various quantities. according to the graph, what is the cost of a single lightbulb?

Looking at the two black dots
5 bulbs cost $9
Divide total cost by number of bulbs bought:
9 / 5 = $1.80 per bulb.
10 bulbs cost $18
Divide total cost by number of bulbs bought:
18 / 10 = $1.80 per bulb
The cost for one bulb is $1.80