log (x+5)+log (x+29)=4
3 3
the 3's are subscripts to log
$\displaystyle \log_3 (x+5)+\log_3 (x+29)=4$
Consider
$\displaystyle \log_ab+\log_ac=\log_a(b\times c)$
So
$\displaystyle \log_3 ((x+5)(x+29))=4$
Raise both sides to the power of 3 gives
$\displaystyle (x+5)(x+29)=3^4$
now you have to solve the quadratic. All good?