What work have you done so far?
I can give you hints..
a) Do you know what the function looks like in a plot of f(x) vs. x? If so, you should have some intuition into the nature of your temperature decay function.
What happens at t=0? You should be able to find the 'y' intercept.
Have you seen a Gaussian before? It is of similar form, , perhaps your graph will look like a bell curve?
b) How do we find max's and min's in calculus? This is where you should take the first derivative, set it equal to 0.
c) Essentially they're asking at what point is the slope greatest. When you hear "slope of a function", your mind should think 'derivatives!'