Dimensional Analysis problem.

I am having such a hard time with this ONE problem. Can anyone help?

The problem:
A well-known night time cold medicine that quiets coughing, relieves sniffling, and soothes sore throat pain contain 25% alcohol by weight. If a patient drinks 30gm of cold medicine, how many grams of alcohol has the patient consumed.

I know it's pathetic, but so far for work I've only gotten;
30 gm x ---------- x ---------- etc = gm of alcohol.
There might be more conversions in between but that's the part I need help with.

I know that the next item on the bottom needs to be gm as well so that they cancel out. But with the percentage and lack of extra information I'm not sure where everything should go. If I knew where everything went I could definitely solve the problem myself.

Thanks so much!

If the cough medicine is 25% by mass, then that means 25 mg of alcohol is present per 100 mg of medicine:

25 mg of alcohol/100 mg of medicine and the patient consumes 30 mg of medicine, so

(25 mg alcohol/100 mg medicine)*30 mg medcine = 7.5 mg alcohol (notice that the "mg medicine" units cancel and you're left with "mg alcohol" on top).

To see it better, I just did:

(25/100)*30 = 7.5

(0.25)*30 = 7.5

Don't forget units!