Jawabanmu

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2013-12-15T21:11:37+07:00
U6 + U9 + U12 + U15 = 40
a + 5b + a + 8b + a + 11b + a + 14b = 40
4a + 38b = 40
2a + 19b = 20
S20 = 10(
2a + 19b)
S20 = 10 (20)
S20 = 200

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