1. Let x be the original amount of baseball cards, 2. half of x was lost so x divided by 2. 3. you buy 18 cards to replace some that were lost 4. You can find the awnser by subtracting 18 from 30, which is 12. 5. Now lets remember that half of your cards were lost. meaning that 12 is only half of what you started with. 6. 12 times 2 would be 24. 7. The Awnser is 24 8. To check your work, you can say x=24, 24 divided by 2 is 12, and 12 plus 18 is 30.
If you think about how it works when cups are stacked. you will begin with the height of the cup plus the height of the lip you would then add just the heigt of the lips until you get to the height needed. so your answer should be 19 cups
