(a) In functional notation, you are asked for C(600).
For this, put 600 where t is in the functional notation C(t).
(b) The value multiplying 8 is 0.5 when the exponent of 0.5 is 1. That is
... t/5730 = 1
Multiplying by 5730 gives
... t = 5730
It will take 5730 years for half the Carbon 14 to be gone.
___
Or, you can recognize a fraction is 1 when its numerator is the same as its denominator. That is t/5730 = 5730/5730 = 1 when t=5730.