The general term of multinomial expansion is α!β!γ!6!(1)α(231)β(321)γ For terms to be rational 3∣β and 2∣γ $\begin{array}{c|c|c|c}
\beta & \gamma & \alpha & \text { Term } \
\hline 0 & 0 & 6 & 1 \
0 & 2 & 4 & 15.3=45 \
0 & 4 & 2 & 15.3^2=135 \
0 & 6 & 0 & 1.3^3=27 \
3 & 0 & 3 & 20.2=40 \
3 & 2 & 1 & 60.2 .3=360 \
6 & 0 & 0 & 1.4=4
\end{array}\RightarrowSumofrationalterms=1+45+135+27+40+360+4=612$