help~`數學

The volume and height of a right circular cone are 108π cm^3 and 9 cm respectively.Find its base radius.

(1/3)πr^2h=108 π
r^2h=324
9r^2=324
r=6 cm
2.一個soild有兩個體,上邊個係cone,下邊個係圓柱體。上邊個係cone slant height is 10cm.下邊個既圓柱體既高度係10cm,個wide係12cm,要計個total surface
area of it(上邊個cone+埋下邊個圓柱體既total surface area)答案係679cm^2(答案係取至三位有效數字)
surface area of cone
= πrl
=π*6*10
=60π
surface area of 圓柱體
=2πrh+πr^2
=2π*6*10+36π
=156π
total surface area
=60π+156π
=216π
=679cm^2