When dealing with decimals, remember the order of places. The first number after the decimal point is the tens place. The second place is the hundredth, and the third is thousandth. Now remember with rounding, if the number proceeding the place is 5 or greater, you round up. Otherwise, you round down.
Now, taking a look at the number, if you want it rounded to a tens place, that's the spot directly after the decimal point. Because the number 5 proceeds the 3 in the tens place, you round up.
The answer is 218.4.
Hope this helps!
