a) 

b)        <<<--- To solve it, apply your calculator or computer . . .  Or apply special tables for logarithms, if you have it. 
                               It is the only way in this case.  // The other way is to expand it in series, but nobody will do it in our days.
                               When you ask other people to do it for you, you simply shift/move your work to their shoulders. 
                               It is not a job for tutors. It is your work.
is the answer -0.8696

c)       <<<--- Apply the formula for the base change for logarithms,  ,  and you will get  =  with decimal logarithms.

                        See the lesson Change of Base Formula for logarithms in this site.
                              
is the answer: 1.588

Thank you so much