Very nice! $$v$$ is the final velocity, $$u$$ is the initial velocity and $$t$$ is the time. As Jerry was initially travelling at $$2.5 \, \mathrm{m/s}$$, $$u = 2.5 \, \mathrm{m/s}$$. As he finally reached a velocity of $$5 \, \mathrm{m/s}$$, $$v = 5 \, \mathrm{m/s}$$. And, as he took a time interval of $$2 \, \mathrm{s}$$ for all this, $$t = 2 \, \mathrm{m/s}$$.
Because we know $$v, \,u$$ and $$t$$, we can calculate $$a$$, the acceleration. Using $$v = u + a*t$$, $$a = \frac{v - u}{t} = \frac{5 - 2.5}{2}$$. From this, we get $$a = 1.25 \, \mathrm{m/s^2}$$.