Step-by-step explanation:
We will use pythagoras' Theorem for this question
[tex] {c}^{2} = {a}^{2} + {b}^{2} [/tex]
where c is the longest side (in this case, the diagonal)
a and b are the 2nd and 3rd longest side (interchangeable)
given a = 10.6, b = 16.8,
[tex] {c}^{2} = {10.6}^{2} + {16.8}^{2} \\ {c}^{2} = 112.36 + 282.24 \\ {c}^{2} = 394.6 \\ c = \sqrt{394.6} \\ = \frac{ \sqrt{9865} }{5} inches[/tex]