bantu y. menggunakan cara.

rata2 = ( 2 × 4 ) + ( 3 × 5 ) + ( 1 × 6 ) + ( 5 × 7 ) + ( 3 × 8 ) + ( x × 9 ) + ( 2 × 10 ) / ( 2 + 3 + 1 + 5 + 3 + x + 2 )
7,2 = ( 8 + 15 + 6 + 35 + 24 + 9x + 20 ) / ( 16 + x )
7,2 × ( 16 + x ) = 108 + 9x
115,2 × 7,2x = 108 + 9x
115,2 - 108 = 9x - 7,2x
7,2 = 1,8x
x = 4

jadi x = 4