Answer: 121.836
Step-by-step explanation: So the first thing you need to do is:
31.24
x3.90 you need to put the zero there because the decimal points would need to match up.
_____
Once you do that just put the decimal down. Like this:
31.24
x3.90
____ Once you do that just ignore the decimal and multiply.
.
Once you have finished, the answer should be 121.836.
Hope I Helped!
:)