Answer:
Hence, the greatest possible whole-number length of the unknown side is:
9 inches
Explanation:
A corollary to the Pythagorean Theorem states that:
If c is the longest side of a acute triangle, a and b are other two sides of a acute triangle then the condition that relates these three sides are given as:

Here we have:
Let a=5 inches.
b=8 inches.
Then,

Hence, to the greatest whole possible whole number length of the unknown side is:
9 inches.