For the reaction, $2 A+B \rightarrow$ products, when the concentration of $A$ and $B$ both were doubled, the rate of the reaction increased from $0.3 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}$ to 2.4 $\mathrm{mol} \mathrm{L}^{-1} \mathrm{~s}^{-1}$. When the concentration of A alone is doubled, the rate increased from $0.3 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}$ to $0.6 \mathrm{~mol} \mathrm{~L}^{-1} \mathrm{~s}^{-1}$. Which one of the following statements is correct