you will always have 21 free CDs so you can put a closed circle on 21 then you can have a max of 15 CDs (180/12) soo put another closed circle on 36
now time for tapes, which is easier, the minimum is 0 and the max is 22.5. Now put closed circles on each and you're done. Except that .5 might get you in trouble, use your own discretion on rather to leave it on the .5 or round. I don't know what your teacher is looking for so I will let you decide.
You cannot add those together because of the variable. Theres no way of knowing what x equals so this is as far as you can go therefor making the answer 3+2x
