Jawapan

2016-04-06T12:08:47+08:00
Isi padu kon = 1/3 × π × j² × t
    120 mm³ = 1/3 × 20 mm × t
         20t = 120 : 1/3
         20t = 120 × 3
         20t = 360
             t = 360/20
             t = 18 mm