Explanation:
11. Plug in -.5 which makes it -1.5+1.75 which is .25
12. -6*-4.3 is a positive since it's two negatives 25.8-5.6 which is 20.2
13. 12*-2.4 which is -28.8-10.5 which is -39.3
14. Rearrange the equation, x=15-6 which is x=9
15. Rearrange again x<15-6 which is x<9 (x is anything less than 9)
16. Rearrange again, except the sign is the other way x>9 (x is anything bigger than 9)
17. Same thing but different sign x≥9 (x is 9 or bigger)
18. Again, x≤9 (x is 9 or smaller)
19. perimeter is just all sides added up. Since it's a rectangle is has 2 of each sides. 10+10+20+20 which is 60 meters
20. Surface area is simply the 2d area of a shape. Width*Lenght 10*20=200 sq ft