Current Attempt in Progress Time standards are now based on atomic clocks. A promising second standard is based on pulsars, which are rotating neutron stars (highly compact stars consisting only of neutrons). Some rotate at a rate that is highly stable, sending out a radio beacon that sweeps briey across Earth once with each rotation, like a lighthouse beacon. Pulsar PSR 1937+21 is an example; it rotates once every 1.55780644887275 i 3 ms, where the trailing :3 indicates the uncertainty in the last decimal place (it does not mean :3 ms). (a) How many times does PSR 1937+21 rotate in 75.0 days? (b) How much time does the pulsar take to rotate 4.00 X 10'5 times and (c) what is the associated uncertainty? (3) Number a Units CD 4? (b) Number Units (c) Number l Units 1