Elimination was used to solve a system of equations. One of the intermediate steps led to the equation 7x=21. Which of the following systems could have led to this equation
A. 8x-y=15, x+y=-6
B.3x+2y=7, 2x-y=7
C.4x+3y=24, -3x-3y=3
D. 7x+2y=21, -7x-2y=21