Answer
See the detailed answer below.
Work Step by Step
$$\color{blue}{\bf [a]}$$
A proton was fired away from a 2 nC point charge when the distance between them was 1mm. If you know that its speed after it is far enough from this point charge [when $r\rightarrow\infty$] was 2.5 Mm/s, what is its releasing speed?
$$\color{blue}{\bf [b]}$$
Solving the given formula for $v_i$;
$$v_i=\color{red}{\bf 1.67\times 10^6}\;\rm m/s$$
