Am doing math and need help, don't understand it

Solve the system of equations. y= 2x y= x^2 - 15

What is best way to getting answer for my exam is

Asurvey of 45 teens found that they spent an average of 25.6 hours per week in front of a screen (television, computer, tablet, phone, based on the survey’s sample mean, which value could be the population mean? 2.3 hours 27.4 hours 75.3 hours 41.5 hours