To solve this system of equations by elimination, what operation could be used to eliminate the x-variable and find the value of y? 2x − 4y = 6 −3x + 3y = 9 a) add 2 times the second equation to 3 times the first equation b) add 3 times the second equation to 2 times the first equation c) subtract 2 times the second equation from 3 times the first equation d) subtract 3 times the second equation from 2 times the first equation