What is the result of adding 2x+7y=4 and -2x-8y=-2

Which of the following situations represents a linear relationship? a. theresa increases the distance she runs by 0.1 miles every week. b. the volume of a box depends on the length of box. c. the amount of money in a bank account increases by 1 percent each year. d. the population of a town doubles every 5 years.

A33 gram sample of a substance that's used to detect explosives has a k-value of 0.1473. n = noekt no = initial mass (at time t = 0) n = mass at time t k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days

Asap! i'm not good math and i'm lost.