Ack! No. The 5.500000 has seven significant digits. The zeroes following the decimal point count since by convention it means that the measurement has been taken to be that precise.
10K probably has infinite significant figures as that's an expression of an exact running distance, not an estimate. The 3.4 miles is probably an estimate (I haven't heard any of any 3.4 mile standard runs - but then I'm not a runner), so it would have two significant figures. But even if 10K and 3.4 had infinite significant digits the number of decimal places you use for the answer would hinge on how precise of a number you use for the conversion between the two units.