tolong ya kak make cara

a = 15
b = 4

Sn = n/2 ( 2a + ( n - 1 ) b )
S₂₀ = 20/2 ( 2(15) + ( 20 - 1 ) 4 )
S₂₀ = 10 ( 30 + 19(4) )
S₂₀ = 10 ( 30 + 76 )
S₂₀ = 10 ( 106 )
S₂₀ = 1060 buah [ opsi. B ]

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