$8\mathrm{.}25.$ The reported $C_{pk},$ for a process with an average of $28,$ a spread of $10$ units, and upper and lower specification limits of $15$ and $35$ respectively, would be:

a$.1\mathrm{.}6$

b$.1\mathrm{.}4$

c$.1\mathrm{.}8$

d$.0\mathrm{.}714$