You just need to memorize the Law of Cooling.

The formula is

Without doing the whole problem for you,

is the temperature of what is being cooled at any time

,

is the temperature of the surrounding area, after you have removed it from being heated.

Are you told

? You did not give it here, and it's pretty important to know.

is the temperature of the object at the moment you have removed it.

Now that you know this, you can use the numbers you are given to solve for the constant

which is the cooling constant.

For part a, simply plug in the new value your given using the

you just found, and solve for

For part b, set

and solve for