There are 7 comedy DVDs, 4 mystery DVDs, and 4 documentary DVDs. What is the probability of randomly selecting a mystery DVD from the cabinet?

Asystem of equations is shown below: 5x + 2y = 3 (equation 1) 2x − 3y = 1 (equation 2) a student wants to prove that if equation 2 is kept unchanged and equation 1 is replaced with the sum of equation 1 and a multiple of equation 2, the solution to the new system of equations is the same as the solution to the original system of equations. if equation 2 is multiplied by 1, which of the following steps should the student use for the proof?