Help me please i need to much the help

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

The highest point on earth is the peak of mount everest if you climb to the top you would be approximately 29,035 feet above sea level at remembering that amount is 5280 feet percentage of the height of the mountain would you have to climb to reach a point 2 miles above sea level

If a and −a are numbers on the number line, which expression must give the distance between them? a) 0 b) a c) |2a| d) |a|