How do you solve log x + log 5 = 2?

use laws of logarithm: ##log AB = log A + log B##; change to single log:
then change to exponential ##x = 20## (Answer)
##log x +log 5 = 2##
##log 5x=2##
exponential form:
##5x = 10^2## (in common log the base is 10)
##5x = 100##
##x = 20## (ans)