Equations of Motion

Which equation is correct for distance $s$ where $u=$ initial velocity, $a=$ acceleration, $t=$ time of journey?

Choose the correct equation of motion.

A bus moving along a straight line at $20 \mathrm{m}/\mathrm{s}$ undergoes an acceleration of $4 \mathrm{m}/{\mathrm{s}}^2$. After $2$ seconds, its speed will be: