if 5^x=y and x is positive, which of the following equals 5y^2 in terms of x? show your work.

thank again for your help and yes b)  5^(2x+1)  ,your note is so important as well I have to be careful the next time 

I really appreciate your working and helping.

y = 5^x

y^2 = (5^x)^2 = 5^(2x)

5y^2 = 5*5^(2x) = (5^1)*(5^2x) = 5^(2x+1)

As long as b) is meant to be 5^(2x+1) not 5^(2x) + 1  then b) is the answer.  Please use brackets to ensure an unambiguous interpretation.