Question 773909
It sounds like you want to solve 2^x = 40 for x


If so, then 


2^x = 40


log(2^x) = log(40) ... apply the log function to both sides


x*log(2) = log(40)


x = log(40)/log(2)


x = 5.32192809488737 ... use a calculator to evaluate


Let me know if this is what you're looking for