To find the smallest decimal, compare place values left to right: ones, tenths, hundredths, thousandths.

Numbers	=	6.058, 6.580, 6.508, 6.085
All have ones digit 6. Compare tenths: 6.058 (0), 6.58 (5), 6.508 (5), 6.085 (0). 0 is smallest, so compare 6.058 and 6.085.
Compare hundredths: 6.058 has 5, 6.085 has 8. 5 < 8, so 6.058 is the smallest.
Smallest	=	6.058