Solution: We need to solve for , which is in the same time units as the compounding, so it will be in months. First, we fill in (1500), (1000), (.06), and (12).
Now divide out the , and simplify :
Take the logarithm of both sides, and remember that :
Divide to get :
To do this, we use Prim's algorithm. First, we mark the edge with the smallest weight (3). Then we take the next smallest weight connected to the already marked edges (4). Then again the smallest connected (5). Finally, we take the (6) which connects the top vertex.