Answer: Third Option

Explanation:
We have the following multiplication of decimal numbers
3.214 mm × 1.5 mm
First multiply

3.214
× 5
-------------
16.07
Now divide the result by 10

Now multiply

3.214
× 1
-------------
3.214
Finally make the following sum
1.607
3.214
-------------
4.821
Finally the answer is the third option
3.214 mm × 1.5 mm= 4.821