Jawabanmu

2014-01-27T21:36:13+07:00
Seminggu = 7 hari
U1 = 80+20(1) = 100
U7 = 80+20(7) = 80+140 = 220

Sn = n/2 (U1 + Un)
S7 = 7/2 (100 +220)
S7 = 7/2 (320)
S7 = 1120