A sigma process with a $1\mathrm{.}5$ sigma shift in its mean has a process capability index of $1\mathrm{.}2.$ Find the process performance index.

a$)0\mathrm{.}5$

b$)0\mathrm{.}7$

c$)1\mathrm{.}2$

d$)3\mathrm{.}6$