A post office always charges a flat one-time fee for any order. One time, Michael sent 35 letters and paid 26 dollars. The next time, he
sent 18 letters and paid $14.10. How much does the post office charge
to send one letter? What is the flat fee?

x = the flat fee = $1.5

y = fee per each letter sent = $0.7

Step-by-step explanation:

Let

x = the flat fee

y = fee per each letter sent

The equations

x + 35y = 26 (1)

x + 18y = 14.10 (2)

Subtract (2) from (1) to eliminate x

35y - 18y = 26 - 14.10

17y = 11.9

y = 11.9/17

y = 0.7

Substitute y = 0.7 into (1)

x + 35y = 26 (1)

x + 35(0.7) = 26

x + 24.5 = 26

x = 26 - 24.5

x = 1.5

x = the flat fee = $1.5

y = fee per each letter sent = $0.7