$1.$ Ten cavemen with a remaining average life expectancy of $10$ years use a path from their cave to a spring some distance away. The path is not easily traveled due to $100$ large stones that could be removed. The annual benefit to each individual if the stones were removed is $$8\mathrm{.}50.$ Each stone can be removed at a cost of $$1\mathrm{.}50.$ The interest rate is $2\%.$a$.$ Compute the benefit$/$cost ratio for the individual if he alone removed the $100$ stones.b$.$ Compute the benefit$/$cost ratio for the individual if the task was undertaken collectively, with each individual removing $10$ stones.