17. A bottle holds x liters of water. If you drink 3 liters, how much water is left?
x - 3
18. There are x students in a class. If 4 students leave, how many students are left?
x - 4
19. A field is x meters wide and 10 meters long. What is the area of the field?
10x
20. Sally has x pounds. She finds 8 more pounds. How much money does she have now?
x + 8
