What is the difference in atomic structure between Lead-205 and Lead-208

What is the molecular formula of a hydrocarbon with m+ = 166? (write the formula with no subscripts, e.g. c4h10.) what is the sum of rings and double bonds in this compound?

Aspirin has a density of 1.40 g/cm3 what is the volume in cubic centimeters of a tablet weighing 320 mg ?

Mike and mitchell decide to have a foot race. they mark off a stretch of 100 yards, and recruit cindy to work the stopwatch. after running the race and looking at the results, cindy declared that mitchell was the fastest. so how did the boys times compare?