tolong bantuannya saya kurang mengerti dri soal ini.

1) u5 = a + 4b = 5
u10 = a + 9b = 15
--------------------------(-)
- 5b = - 10
b = 2
a + 4b = 5
a + 4(2) = 5
a = 5 - 8
a = - 3
u20 = a + 19b
= - 3 + 19(2)
= - 3 + 38
= 35 (C)

2) u3 = a + 2b = 16
u6 = a + 5b = 7
--------------------------(-)
- 3b = 9
b = - 3
a + 2b = 16
a + 2(-3) = 16
a = 16 + 6
a = 22 (C)