You can
put this solution on YOUR website!Good question. Great question. Let's go through it.
So, we start of with the equation B=100e^kt, and the fact that B=5287 when t=13. With this in mind we can easily solve for k as shown below:

(divide both sides by 100)

(natural log of both sides, which cancels out the e)

(divide both sides by 13)

(to three significant figures)
Hope all that helps.