Find value of -2/3y-3/4=5

Use the elimination method to find the solution to the system of equations. 2x - 3y = -9 -x + 3y = 6

The center of a circle represent by the equation (x+9)^2+(y-6)^2=10^2 (-9,6), (-6,9), (6,-9) ,(9,-6)

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?