a$)$ Un$-$pipelined

Here for $7$ stage it is $4+4+4+1+1+1+1=16$ units

Herewe are simply adding the time units for each stage. $($IF$,$ OL$,$ OS$)=4$ units rest all have $1$ units of time

b$)$ pipeline $=$ max$(4,4,4,1,1,1,)+2$

it is $4+2=6$ units

Here we will take maximum time for all steps and then $2$ is added as an overhead.

c$)$ speed up $=$ non$-$pipleine $/$ pipeline $=16/6=2\mathrm{.}67$ units

Answer

This is how it is solved.