Ciera adds equations 1 and 2 together to solve this system of equations. why is this method generally valid for solving a system of equations?

Which of the following expressions are equivalent ?

Dylan and dusty plan to take weekly surfing lessons together. if the 2-hour lessons are $20 per person and they plan to spend $100 each on new surfboards, what is the maximum number of lessons the two can take if the total amount spent for lessons and surfboards is at most $480?

Which inequality statement describes the two numbers on a number line? "? 7 and a number 5 units to the right of ? 7"