Can someone help me understand this problem?

Give a formula to predict the running time of a program for a problem of size N
when doubling experiments have shown that the doubling factor is 2^b and the running
time for problems of size N0 is T.

I don't get what they mean by the doubling factor or what b is supposed to be. And what's the difference between N0 and N exactly?

Question

Can someone help me understand this problem? 

Give a formula to predict the running time of a program for a problem of size N
when doubling experiments have shown that the doubling factor is 2^b and the running
time for problems of size N0 is T.

I don't get what they mean by the doubling factor or what b is supposed to be. And what's the difference between N0 and N exactly?

phi · Answer

I think b is the number of doublings.  b= log_2(N)/log_2(N0)
N0 is some size that takes time T to execute.