Solve the Problem $\mathrm { D } = \sqrt { \mathrm { L } ^ { 2 } + \mathrm { W } ^ { 2 } + \mathrm { H } ^ { 2 } }$

Solve the problem.
-The length of the diagonal of a box is given by $\mathrm { D } = \sqrt { \mathrm { L } ^ { 2 } + \mathrm { W } ^ { 2 } + \mathrm { H } ^ { 2 } }$ where L, W, and H are the length, width, and height of the box. Find the length of the diagonal, D, of a box that is 5 ft long, 4 ft high, and 6 ft wide. Give the exact value.

A) $\sqrt{77} \mathrm{ft}$
B) $15 \mathrm{ft}$
C) $2 \sqrt{30} \mathrm{ft}$
D) $120 \mathrm{ft}$