The floor of a round hut has a diameter of 6meters. What is the floor's circumference?

The most commonly used equation for circumference is
C=2πr.  Where c is the circumference, π is pi (or 3.14159...), and r is the
radius.

In your equation, you are given diameter.  Remember
that the radius is half of the diameter.  So, in this case, the radius, r, is half of 6,
or 3 meters.

Now, substitute the radius into the equation
for circumference, and you get:

C=
2π(3)

= approximately 18.84
meters

What you know have found is the distance
around the circle.