Hello me again.. Can someone help me porfavor?

(98 points) i need with 5 questions. answer definitions are welcomed, but not necessary.

Two customers went to a post office. first customer paid $12 for 14 and 5 envelopes the second paid 24.80 for 10 postcards and 15 envelopes. what is cost of each envelope?

Evaluate cos2θ for cosθ = square root of 3/2