Answer65.
Explanation:
In this question, we are asked to state the distance between third and first frets.
Now, to consider this distance, just visualize. From the particulars in the question we can see that to get the distance, we need to add the two numbers together.
Mathematically, to calculate the distance, we need to make addition. This is represented by 31.749 + 33.641 = 65.39mm
The distance between the first fret and the second fret is 65.39mm