The stack of cards are 1 inch tall all together taking up 8 inch’s (cubed)or half of the space
For this case we have the following type of equations:
Quadratic equation:

Linear equation:

We observe that when equating the equations we have:

Rewriting we have:

We obtain a polynomial of second degree, therefore, the maximum number of solutions that we can obtain is 2.
Answer:
The greatest number of possible solutions to this system is:
c.2
Hey there!
12 ≥ 5f - 18
5f - 18 ≤ 12
ADD 18 to BOTH SIDES
5f - 18 + 18 ≤ 12 + 18
SIMPLIFY IT!
5f ≤ 30
DIVIDE 5 to BOTH SIDES
5f/5 ≤ 30/5
SIMPLIFY IT!
f ≤ 6
Therefore, your answer is: f ≤ 6
Good luck on your assignment & enjoy your day!
~Amphitrite1040:)