no 6 gimana caranya??

( a + b + c ) / 3 = 8
a = ?

( a + b ) / 2 = 7.5
a + b = 7.5 × 2
a + b = 15
a = 15 - b
b = 15 - a

( b + c ) / 2 = 8
b + c = 8 × 2
b + c = 16

a + b = 15
c + b = 16
(eliminasi)
a - c = - 1
c = a + 1
b = 15 - a

( a + 15 - a + a + 1 )/3 = 8
a + 16 = 3 × 8
a + 16 = 24
a = 24 - 16
a = 8

Jadi, nilai ulangan pertama Rudi adalah 8.