2 times 10 is 20. 2 times x is 2x. 2 times -4 is -8. So that gives you 20+2x-8. Combine like terms, so you don't have anything that matches with 2x, so you leave that aside. So you subtract/add 20-8 which gives you 12 and add the 2x on that. So the full answer is 2x+12.
