If you need help with the question I'd recommend posting your working thus far? I can't really see whether you're asking for it or if you simply wish for an answer since it isn't provided :_;
To start with this, remember the formulae that associates half-life and the decay constant, lambda, i.e. const. decay = (ln(2))/T(half life) and then look back at the definition of the decay constant: that'll let you solve the first part.
The second is a question regarding decay with a constant rate, i.e. analogous to moving a distance at constant velocity and finding the time.