Hi,
First figure out how many seconds are in a year and multiply that by 3.8 to turn it into km/year
60 sec in min
60 sec * 60 = 3600 sec in an hour
3600 sec * 24 = 86,400 sec in a day
86,400 * 365 = 31,536,000 sec in a year
The term is now 31,536,000 km/year and we need to get it to miles
1 km = .6214 miles so we must now multiply our term by .6214 to convert it to miles
31,536,000 * .6214 = 19,596,470.4
Now our term is 19,596,470.4 miles/year and thats your answer!
If you want an even more precise answer you could be more detailed and say 1 km = .621371 miles and then our final term would come out as 19,595,555.856 miles/year
I hope this helps!
btw i did assume a 365 day year