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Volume of a sphere is  4/3 pi r^3

4/3 pi (r^3) = 4.5

 

r^3 = (4.5 x 3/4 )/ pi

r^3 =1.07429586

r= 1.024176 units     (you didn't specify units in your question)  

Think of this formula V=(4/3)πr³

 

4.5=(4/3)πr³

13.5=4(πr³)

3.375=πr³

3.375/π=r³

∛(3.375/π)=r