18. 3(-x+5)+4x
-3x+15+4x
=x+15
19. 2x+7-2(x-4)
2x+7-2x-8
=1
20. 3x-2(x+3)+6
3x-2x+6+6
=x+12
21. The distributive property is when you take the number before the parenthesis and multiply both numbers inside the parentheses by that number (this only works if you are multiplying the number if the number is divided, added, subtracted,etc. this process will not work)
