To express 0.015849 to three significant figures, we start counting significant figures from the first non-zero digit.
The number 0.015849 has the significant digits 1, 5, and 8.
Rounding 0.015849 to three significant figures gives us:
0.0158 (the 4 in 0.015849 rounds the 8 down).
So, 0.015849 correct to three significant figures is 0.0158.