Jawabanmu

2014-08-23T19:45:31+07:00
U4 = a + 3b = 91

U6 = a + 5b = 85

Dieliminasi shg 2b = -6 --> b=-3
Substitusi nilai b, shg a = 100

U20 = a+19b = 100-57 = 43