
$\begin{aligned}
& \text { Area }=\frac{1}{2}\left|\begin{array}{ccc}
\hat{i} & \hat{j} & \hat{k} \
1 & 2 & -7 \
6 & d & -2
\end{array}\right|=15 \sqrt{2} \
& (-4+7 d) \hat{i}-\hat{j}(-2+42)+\hat{k}(d-12) \
& (7 d-4)^2+(40)^2+(d-12)^2=1800 \
& 50 d^2-80 d-40=0 \
& 5 d^2-8 d-4=0 \
& 5 d^2-10 d-2 d-4 \
& 5 d(d-2)+2(d-2)=0 \
& d=2 \text { or } d=-\frac{2}{5} \
& \because d>0, d=2 \
& (a+1) \hat{i}+(b+2) \hat{j}+(c-7) \hat{k}=6 \hat{i}+2 \hat{j}-2 \hat{k} \
& a+1=6 & b+2=2, c-7=-2 \
& a=5 \quad b=0 \quad c=5 \
& |A B|=\sqrt{1+4+49}=\sqrt{54} \
& |B C|=\sqrt{25+25}=\sqrt{50} \
& |A C|=\sqrt{86+4+4}=\sqrt{44}
\end{aligned}$
Ans. 54