79958.42
rounded to 3 shouldnt it be like 8.00 or 80.0?
No, after all think about how far 8 and 80 are from 79958.42
What you should do is convert to standard form: $\displaystyle 7.995842 \times 10^4$
You can then round off the first part to 3sf which is 8.00 but you must bring back the 10^4 to give $\displaystyle 8 \times 10^4 = 80000$
79958.42
Remember that with significant figures, 0 counts in the context of a 10 or 100 and so forth, so for example, in 405, the 0 is significant, whereas in 0423, the 0 is not significant.
Therefore, when rounding this to three significant figures, the answer is 80000, as e^(i*pi) said.