Word problem. Need help please?

Roberto and Mia are traveling to the United States. They are buying postage for postcards to send to their friends in Canada and Mexico. Mia spends $6.10 on postage to send 8 postcards to Mexico and 3 postcards to Canada. Roberto spends $10.90 to send 5 postcards to Mexico and 12 postcards to Canada. What is the postage rate for the postcards sent to Mexico?