Does this mean that the radius is the input aka 3 ? what about the PI ?

Explanation:

In  this question

d is known as diameter

r is known as radius

c is known as circumference

pi is known as π

a is known as area

Now, In Maths

Area of circle = π×r×r

Circumference of circle = 2×π×r

Radius (r) = diameter(d)÷2

Given diameter is 6

then, r = 6 ÷2

r = 3

so, diameter = 6

radius = 3

circumference = 2×π×r

                        = 2×3.14×3 ( the value of π is equal to 3.14)

                        = 18.84

Area = π×r×r

= 3.14×3×3 ( the value of π is equal to 3.14)

 = 28.26