An engineer has been offered an investment opportunity that will require an immediate cash outlay of $$40,000$ for a cash inflow of $$3500$ for each year of investment. However, she must state now the number of years she plans to retain the investment. Additionally, if the investment is retained for $6$ years, a lump$-$sum amount of $$42,000$ will be returned to her; after $10$ years, the lump$-$sum return is anticipated to be $$49,500,$ and after $15$ years, it is estimated to be $$56,000.$ Money is currently worth $12\%$ per year. Determine the present worth values for $6$ years, $10$ years, and $15$ years, and decide if the decision is sensitive to the retention period?

The present worth when the investment is retained for $6$ years is $ $.$

The present worth when the investment is retained for $10$ years is $ $.$

The present worth when the investment is retained for $15$ years is $