We can solve this by using:
[tex]\vec{v}=\vec{v_0}t+\frac{1}{2}\vec{a}t^2[/tex]
Plug in the numbers:
[tex]\vec{v}=25\mathrm{\frac{m}{s}}\cdot3\mathrm{s}+\frac{1}{2}\cdot5\mathrm{\frac{m}{s^2}}\cdot (3\mathrm{s})^2=\boxed{97.5\mathrm{\frac{m}{s}}}[/tex]
Hope this helps.
