有關f2數學問題!

May makes a dozen small candles melt and recast it into a large cylindrical candle of height 20 cm. If each small candle is a cylinder of radius 1 cm and height 9cm, find the radius of the large candle formed.
Volume of a candle = πr2h
Volume of each small candle = π(12)(9) = 9π cm3
Volume of 12 small candles = 9π * 12 = 108π cm3
Let the radius of the large candle be r
Volume of large candle = πr2(20) = 108π
20πr2 = 108π
r2 = 5.4
r = √5.4 = 2.32cm

Total Volume of small candles = Volume of large candle

Let the Radius of the large candle be R

(12)(9)(pi)(1^2) = (20)(pi)(R^2)
108 = 20(R^2)
R = 2.3 cm