Mohon dengan caranya

Lebih cepat pakai the king

Nomor 7
U7 = 42
a + (n-1) b = 42
a + (7-1) b = 42
a + 6b = 42

U14 = 77
a + (n-1) b = 77
a + (14-1) b = 77
a + 13b = 77

Eliminasi a dari pers 1 dan 2
a + 6b = 42
a + 13b = 77 (dikurang)
-7b = -35
b = -35/-7
b = 5

Substitusi b ke pers 1
a + 6b = 42
a + 6.5= 42
a + 30 = 42
a = 42 - 30
a = 12

U20 = a + (n-1) b
= 12 + (20-1) 5
= 12 + (19) 5
= 12 + 95
= 107 (A)

Maaf kalo salah -'
Semoga membantu :)