Solution:
In right triangle depicted in the diagram
Hypotenuse = 9 cm
Base = 6 cm
As we know ,By pythagoras theorem
(Hypotenuse)²= (Base)² + (Altitude)²
⇒9²= 6² + (Altitude)²
⇒81 - 36= (Altitude)²
⇒ (Altitude)²= 45
⇒ Altitude = √45=
cm
So, Altitude = 5 × 1.732= 8.660 cm
So, Approximate minimum height of shelf so that box can fit in the picture described = 8 centimeters