Which table shows a function that is decreasing only over the interval (–1, ∞)?

Use the graph of the sine function y=2sinθ shown below

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?

I’m really confused and need to learn this