how do you perform this??

log x + log(x+3) = 1

One of the main rules of logs is

Log(AB) = Log A + Log B, as long as the base is the same

so log x + log(x+3) = 1
Log (x(x+3)) = 1
Log(x^2 + 3x) = 1
x^2 + 3x = 10^1
x^2 + 3x - 10 = 0
(x+5)(x-2) = 0

x=-5 or x=2

but in log x , x must be greater than 0
so x = 2