For a given chemical reaction

$\gamma$₁A + $\gamma$₂B $\to$ $\gamma$₃C + $\gamma$₄D

Concentration of C changes from 10 mmol dm^$-$3 to 20 mmol dm^$-$3 in 10 seconds. Rate of appearance of D is 1.5 times the rate of disappearance of B which is twice the rate of disappearance A. The rate of appearance of D has been experimentally determined to be 9 mmol dm^$-$3 s^$-$1. Therefore, the rate of reaction is _____________ mmol dm^$-$3 s^$-$1. (Nearest Integer)