A fraction is simply a simpler way of putting a decimal, as it represents the division. Example, when something is half, or .5, it can be described as one divided by two, or 1/2
Since 3.5 is three, and a half, sum the two of them and you get 3 1/2, or, multiply 3 by 2 and get 6, and add that to 1 to get seven
You will get 7/2