Hello,
Solution for your question is:
4/3 π (R^3- r^3)ρmg = 4/3 π R ^3 ρwg
1- (r/ R) ^3 =8 / 27
r /R =( 19/27)^1/3= 19^1/3 /3
=0.88 =8/9
Hope it helps
Feel free to ask if you have any questions
Good luck!
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