Which notation correctly represents instantaneous velocity when $x\left(t\right)$ is a position function?

A cart moves along a track with position $x\left(t\right)=2t^5-t^3+4t-8$ meters. Which expression gives its instantaneous velocity function?

An object has $x\left(1\right)=7$ $\text{m}$ and velocity $v\left(t\right)=3t^2+2$ $\text{m/s}$. What is $x\left(4\right)$?

Which unit is appropriate for acceleration in SI units?

What does the definite integral ${\int }_{t1}^{t2}a\left(t\right)dt$ represent physically?

An engineer knows $a\left(t\right)$ and wants to reconstruct $x\left(t\right)$. Which sequence of operations is required, along with the needed information?