tolong dibantu... no 38 ama 40 pake cara

38 ) dik a = 10 , b = 2
dit s15 = ...?
sn = 1/2n(2a+(n-1)b)
s15 = 1/2x15(2.10+(15-1)2)
s15 = 15/2(20+28)
s15 = 15/2x48
s15 = 15x24
s15 = 39

40) bunga 5% = 4.000.000 x5/100 = Rp 200.000
bunga yg didapat = 4.300.000-4.000.000 = Rp300.000

300.000/200.000 = 2/3 tahun atau 2/3x12 bulan = 24/3 = 8 bulan