Answer :

3.5 pound = 3 5/10 pounds = 3 1/2 pounds 
Now, 1 pound = 16 ounces, so 1/2 pound = 16*1/2 = 8 oz

So the answer is 3 pounds and 8 oz.
The question is asking to calculate how many is 3 1/2 pounds written as combination of whole pounds and whole ounces, base on the said given and in my further calculation, the possible answer would be 3 pounds and 8 ounces. I hope you are satisfied with my answer