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18). W = J :K
W = 60 : 80
W = 3/4 × 60
W = 45menit
09.30 + 45
=10.15

19).Lpermukaan
=(2×12 ×6) + (2 × 12 × 7 ) + (2 × 7×6)
=144 + 168 + 84
=396cm²

20).V = π×r² × t
V = 3,14 × 8 × 8 × 30
V = 3,14 × 64 × 30
V =6028,8cm³