Which equation combines with the given equation to form a system of equations with the solution $x=3$ and $y=9$?



$x+2 y=21$

A$4 x+6 y=64$

B$2 x+y=36$

C$4 x+y=21$

D$-3 x+4 y=33$

E$3 x+2 y=28$