Figure 2-44 gives the acceleration $a$ versus time $t$ for a particle moving along an $x$ axis. The $a$ -axis scale is set by $a_{s}=12.0 \mathrm{~m} / \mathrm{s}^{2} .$ At $t=-2.0 \mathrm{~s}$ the particle's velocity is $7.0$ $\mathrm{m} / \mathrm{s}$. What is its velocity at $t=$ $6.0 \mathrm{~s} ?$