Answer:
d = 10 inches
Explanation:
It is given that,
The length, breadth and the height of a rectangular box is 8 inches×10 inches ×6 inches
We need to find the length of its longest diagonal.
In a rectangle, 6 inches will act as perpendicular and 8 inches will be base. The diagonal can be calculated using Pythagoras theorem as follows :

So, the length of its diagonal is 10 inches.