Theoretical speedup of a program that is $75\%$ parallel and $25\%$ serial on $3$ processing cores is

Question $4$ options:

a$\mathrm{.}3$

b$\mathrm{.}2\mathrm{.}75$

c$\mathrm{.}2\mathrm{.}5$

d$\mathrm{.}2$