Remember that r1/r2 is INVERSELY PROPORTIONAL!!!!! to the square root of M2/M1, therefore if you square both sides you end up with 5625/23409 for you r1/r2 and x/20.18 for you M2/M1 no to solve you x...
It is between 16 and 88s
There are 60 nano-seconds in a second. :)
There are an infinite number of them between 21 and 22. Here are three of them: 21.0000001 21.0000002 21.9999999
21.03, 21.05, 21.07 is the answer