I got this right so i skimmed over it when I reviewed last time, but i just noticed that although I got the exact number I went about it a slightly diff way. If you notice when they calculate the net investable assets at Time 1, they deduct only the debt and mortgage amount, but make no adjustments for the current year salary, expenses, and mortgage payments (they pay the mortgage at year end, so they still have one year of mortgage payments).
Coincidentally, the after tax salary of 475 totally offsets the mortgage plus time zero living expenses of (250 + 225), so the effect is the same as they have calculated, but it makes me wonder if there had been a variance if I did it wrong.
I am highly confident I am correct, and they should have at least shown these calculations even though the net effect was the same, just so we could see how to do it if there was a net positive or negative effect. However, please correct me if I am wrong.