When solving logarithmic/natural log equations, the strategy is to get ln (x) alone on one side, and all the stuff on the other side. Then exponentiate both sides to get to x.
2 ln (x + 3) = 0
ln (x + 3) = 0
At this point, we can't isolate anymore or use logarithm properties to separate this further. But we have ln (something), and we can exponentiate.
x+3 = 1 <--This come from the fact the ln (x) and are inverse functions that undo each other. This is why exponentiating works.