To the nearest whole number meaning without fractions, or in this case decimals. In the tenths place we have the # 5. When rounding, if the number to the right of your rounding place( to the nearest tenth, hundredth, whole #, ect.) , is higher than 4 then you increase the rounding place # by 1. If it is lower than the 4 then the rounding place # stays the same. So your answer is 850.
sorry for the horrible explanation.
