Circumference = 2 Pi r
Circumference = Pi d
Pi is roughly 3.14159
r is the radius, the distance from the middle of the circle to the edge.
The diameter (d) of a circle is the distance across the circle, from edge to edge, going through the middle.
diameter = 2 * radius
d = 2 * r
Your question says "a circle is 4.5 ft" but it doesn't say if that 4.5 is the radius or diameter.
If the radius is 4.5 ft then
C = 2 * 3.14159 * 4.5
C = 28.27431
rounded to the hundredths place
C = 28.27 ft
If the diameter is 4.5 ft then
d = 4.5 = 2 * r
4.5 = 2 * r
r = 2.25
C = 2 Pi r
C = 2 * 3.14159 * 2.25
C = 14.137155
round to the hundredths place
C = 14.14