Find the surface area of the prism

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?

Libby built a fence that was 56 \text { feet}56 feet long over 44 days. she built the same length of fence each day. how many inches of fence did libby build each day?

When you find the area of a triangle do you use in. or in2