If you have 80 dollars then get 20 more what is the percent change?

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 fraction is not equivalent to 8/12 a. 2/3 b. 24/36 c. 4/10 d. 6/10

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10