Answer:
10.2 inches.
Explanation:
First, assume the two sides are legs, square both sides and add them,:
144+225=369
square root of 369 is the hypotenuse
suppose 15 is the hypotenuse (it can't be 12 since the hypotenuse is the longest)
Then 12^2+x^2=15^2
x^2=81
x=9, a 9-12-15 right triangle.
So the third side can be 9 or square root of 369 =19.2 to nearest tenth.
The difference is 19.2-9=10.2 inches.