17. negative numbers are closed under addition.
18. prime numbers are closed under subtraction.

The nature park has a pride of 5 adult lions and 3 cubs. the adults eat 8 pounds of meat each day and the cubs eat 4 pounds. how much meat do the cubs and lions eat?

What is the value of x in the following equation. -x ^3/2 = -27

Solve this 364x-64x=300x and 12(x2–x–1)+13(x2–x–1)=25(x2–x–1)