Answer
$v = 30 ~m/s$
Work Step by Step
The change in velocity will be equal to the area between the acceleration versus time graph and the x-axis. Therefore,
$\Delta v = \frac{1}{2}(10~m/s^2)(6~s)$
$\Delta v = 30~m/s$
We can then find the velocity at t = 6 s;
$v = v_0 + \Delta v$
$v = 0 + 30~m/s$
$v = 30 ~m/s$
