Hello!
Decimals used to confuse me a lot! :D
When a question asks to round the decimal to the "nearest tenth", it simply means to round it to one decimal place.
6.7086 would be rounded to 6.7 if we round it to the nearest tenth. See, the 7 is in one place after the decimal point.
The best way to understand decimal places, in my opinion, is to search up a tenths, hundredths, thousandths, etc. chart. Hope this gave you a better understanding of decimal places!