It cost Cai $1.80 to send 12 text messages. How much would it cost to send 90 text messages?

Answer 1

90/12 = 7.5

7.5 x 1.8 = $13,50 for 90 messages

1.8 for 12

means 1.8/12 = 0.15 for one message

90 x .15 = $13.50 for 90 messages

the ratio of money to messages is a constant

C/90 = 1.8/12

C = 1.8(90)/12 = $13.50