A post office always charges a flat one-time fee for any order. One time, Micheal sent 35 leters 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?

Can someone check if i did this correct. it’s number 4 if you’re wondering.

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.

Simplify the algebraic expression 8y-2(y+4)