Cara ngerjain nomer 7 kak

U6 = a + 5b
U8 = a + 7b

U6 + U8 = 72
2a + 12b = 72
a + 6b = 36

U5 = a + 4b = 26

a + 6b = 36
a + 4b = 26
2b = 10
b = 5

U10 = a+9b = ...
a + 9b = (a + 6b) + 3b
= 36 + 3(5)
= 51 (C)