'round your answer to 3 decimal places' means that it wants you to show three numbers after the decimal point, so...
π = 3.141592....
you want 3 numbers after the bullet point so...
3.141
but you have to take into consideration the number after the 3rd number after the bullet point, so...
if it is greater than 5 you round the number in front of it up, if it is less than 5 you round the number in front of it down. so...
3.141 is rounded up to 3.142 because the number after the 3rd number is more than 5
