Figure $1$: Velocity versus Time Plot of an Object

$2.)(6$ points$)$ Answer the following questions based on the velocity versus time plot of an object undergoing motion in one dimension $($see Figure $1).$

a$.)$ What is the velocity of the object at $4$ s $?$

b$.)$ What is the velocity of the object at $11\mathrm{.}5$ s $?$

c$.)$ What was the acceleration of the object at $8\mathrm{.}5$ s $?$

d$.)$ What was the acceleration of the object at $2\mathrm{.}5$ s $?$

e$.)$ What was the displacement of the object over the first $8$ s $?$

f$.)$ What was the average acceleration of the object over the entire $15$ s$?$