What is ten times the sum of half a number and 6 is 8

  lets use x The sum of that and 6 is          1/2 x + 6

Ten times that is              10 (1/2 x + 6)

The question says that's 8.
                                        So       10 (1/2 x + 6) = 8

Divide each side by  10 :                1/2 x + 6  =  0.8

Subtract  6  from each side:            1/2 x  =  - 5.2

Multiply each side by  2 :                        x  =  - 10.4