So first we use x and twice means 2, meaning 2x and we have plus 8, which is 2x + 8, and the sum as -10 would be = -10, or 2x + 8 = -10. Now we subtract 8 from -10 (plus will change to subtract), giving us 2x = -18. Then instead of multiplying -18 to get x, we divide -18, giving us -9, and so that will be our answer for x, as in x = -9.
Hope this helped!
Nate