What the question is asking you to do is to (say) calculate 20% of 120 grams.
(20/100) * 120 = 20 * 120 / 100 = 2400 / 100 = 24 grams of Ketoprofen
(2/100) * 120 = 240/ 100 = 2.4 grams of cyclbenzprine.
(2/100) * 120 = 2.4 grams of baclofen
The total amount of the active ingredients is 28.8 grams.
The rest is (say) water or something that is inactive.
120 - 28.8 = 91.2 grams of inactive material. You don't need to know this, but it might explain why this question gave you trouble.