It is just a matter of formula
Attachment:
GRE For the rectangular solid above.jpg [ 21.98 KiB | Viewed 857 times ]
First find the diagonal of the rectangle which is the base of the entire solid (red line
\(11^2+7^2=121+49=\sqrt{170} \approx 13.03\)
Then find the diagonal with the same process using the diagonal (red line) + the height (blue line)
\(13.03^2+8^2=169.7+64 \approx 233.7 \)
Answer is 234
Two easy steps