Derrick adds equations a and b to solve this system of equations. what makes this approach a valid method in general for solving a system of equations? equation a: 5x+4y=24, equation b: 3x-4y=16 choices: a. as long as addition is used on both sides or subtraction is used on both sides, a true equation will remain true. b. adding a quantity like 5x+4y to one side of an equation and another quantity like 24 to the other side maintains the equality if the two quantities are equal. c. because the y-terms cancel: (5x+4y)+(3x−4y)=5x+3x+4y−4y=8x  ;   d. the method will give the correct solution, x=5x=5, and y=-14y=-14. 5(5)+4(-1/4)=24 3(5)−4(-1/4)=16