A rectangular solid has dimensions $3 \times 4 \times 6$. What is its **diagonal** (the longest straight line that fits inside)?

The space diagonal of a rectangular solid with dimensions $\ell \times w \times h$ is $\sqrt{\ell^{2} + w^{2} + h^{2}}$. $\sqrt{3^{2} + 4^{2} + 6^{2}} = \sqrt{9 + 16 + 36} = \sqrt{61}$. - Trap D ($13 = 3 + 4 + 6$) adds dimensions. - Trap A and B come from miscombining squares.