Question

At the market, 5 light bulbs cost $9dollar  How much do 7 light bulbs cost?

Answer 1

9/5= 1.80
1.80x5= 9 
so, each light bulb costs 1.80
1.80x7=12.6
the answer is 12.6

Answer 2

Good question!

Quoted answers are NOT Mine! All sources / further information provided:

"The answer is $12.60, because:
 $9/ 5 lightbulbs is $1.80 per lightbulb.
Next, you take the $1.80 per light bulb and multiply it by 7 lightbulbs."

Source / further information may be provided at: 

brainly.com/question/7418849

I take NO credit for this answer.  Credits reserved to @covered0209

I am only here to help, not to get into trouble.  I hope you understand