Can you help me with this math pleasee

Find the solution of this system of equation -7x+y=-20 9x-3y=36

2people are trying different phones to see which one has the better talk time. chatlong has an average of 18 hours with a standard deviation of 2 hours and talk-a-lot has an average of 20 hours with a standard deviation of 3. the two people who tested their phones both got 20 hours of use on their phones. for the z-scores i got 1 for the chatlong company and 0 for talk-a-lot. what is the percentile for each z-score?

X+ y = 5 ; x - y =3 solve using linear combination