Which of the following numbers is rational?

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?

Find the pattern and use it to list the nth term in the sequence. 6, 12, 20, 30, 42, 56, the nth term of the sequence is

Which ordered pair is a solution to the system of linear equations? 2x + 3y= 6 –3x + 5y = 10