You would do the opposite of subtracting which is adding to -10 so add 10 to -10 and add 10 to -20. The -10 now equals 0 so we can get rid of that. Now we have 5x=-10. To get rid of the 5, do the opposite of multiplying and divide 5 from 5x and divide 5 from -10. We now have x=-2! This is your final answer!