#### Answer

radius = 1.5 cm
diameter = 3 cm

#### Work Step by Step

The area of the circle = 2.25$\pi cm^{2}$
The area A of a circle whose radius has length r is given by
A = $\pi r^{2}$
2.25$\pi$ = $\pi r^{2}$
2.25 = $r^{2}$
r = 1.5 cm
Therefore diameter of the circle = 2r = 2* 1.5 = 3 cm