$\begin{array}{1 1} 6.^{11}P_9 \\ 12.^{11}P_9 \\ 24.^{11}P_9 \\ 30.^{11}P_9 \end{array}$

There are 14 seats, 3 girls and 9 boys.

3 girls can be seated in backrow in the seats numbered 1,2,3 or 2,3,4. (in 2 ways in $1^{st}$ van.)

Similarly in two ways they can be seated in other van.

Girls among themselves can be arranged in $3!$ ways.

After fixing girls remaining 11 seats are to be occupied by 9 boys in

$^{11}P_9$ ways.

$\therefore$ The required no. of arrangements = $4.3!.^{11}P_9=24.^{11}P_9$

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