Can someone please explain how to do this?

While scuba diving, rajeev dove to a depth of 12.6 feet below the surface of the water and then descended another 8.7 feet. what expression can be used to find rajeev's new position? 12.6 – 8.7 –12.6 – 8.7 –12.6 – (–8.7) 12.6 – (–8.7)

What is the result of adding the system of equations? 2x+y=4 3x-y=6

Which value of m will create a system of parallel lines with no solution? y= mx - 6 8x - 4y = 12