At the market 5 light bulbs cost 9 dollars how mush does 7 light bulbs cost?

So first off we need to figure out how much each light bulb cost. So 5 divided by 9 = 1.8. so each light bulb cost $1.80. To figure out how many 7 light bulbs cost multiply 7 by 1.8 which equals 12.6. So 7 light bulbs cost $12.60