Answer:
P + H ≥ 20
P*0.8 lb + H*1.3 lb ≤ 30lb
Step-by-step explanation:
Let's define H as the number of hardcover books.
Let's define P as the number of paperback books.
Now we have the restrictions:
"... so that there are at least 20 books in each box..."
Then:
P + H ≥ 20 (the total number of books per box is 20 or larger)
"...but the boxes cannot weigh more than 30 pounds."
P*0.8 lb + H*1.3 lb ≤ 30lb (the maximum weight that we can have in the box is 30 pounds)
Then the set of constraints is:
P + H ≥ 20
P*0.8 lb + H*1.3 lb ≤ 30lb
Notice that this system has a lot of possible solutions.
P = 20 and H = 0 is a solution
P = 21 and H = 0 is a solution.
P = 19 and H = 1 is a solution.
etc...
