Jawabanmu

2014-03-19T12:25:13+07:00
Sn  = n 2 + 5 n
S20 = 20. 2 + 5 . 20
       = 40 + 100
       = 140
2014-03-19T12:28:03+07:00
Sn = 2n + 5n
     = 2.20 + 5.20
     = 40 + 100
     = 140