8115 has 15 in its denominator.
15=3×5
To make the fraction a terminating decimal, we need to eliminate 3 in the denominator by multiplying a number that is a multiple of 3.
Since we are asked for the smallest such natural number, we go with 3 itself.
8115×3=8×15+13×5×3=1215
Now, the denominator is a multiple of 5. Hence, it will result in a terminating decimal number.
In fact,1215=24.2, which is a terminating decimal.