Anyone help? please!!

What is the solution to the system of the equations? x = y - 3 x + 3y = 13

What number should be added to both sides of the equation to complete this square? x^2-10x=7

Liz is shipping a package to her friend.the maximum weight of a medium flat-rate box is 20 pounds,including the box which weighs 6 ounces.write and solve an inequality to describe the possible weight ,w, of the contents that liz will ship to her friend if she must use a medium flat-rate box.