it is 639.5. this is how you round numbers to the nearest tenth:
if the digit in the hundredths place is 5 or more you round up one, if it is lower than 5 it stays the same, pay no attention to the thousandths place....ex--> 0.497
the 4 is the tenths place
th 9 is the hundredths place
the 7 is the thousandths place......since 9 is 5 or more you round the 4 up one number, so the 4 would be a 5. pay no attention to the 7. lets do another
0.426
the 4 stays as a 4 because 2 is a lower number than 5.