Awesome, as Jerry was initially travelling at 2.5 m/s, $$u = 2.5 \, \mathrm{m/s}$$. As he finally reached a velocity of 5 m/s, $$v = 5 \, \mathrm{m/s}$$. And, as he took a time interval of 2 s for all this, $$t = 2 \, \mathrm{m/s}$$. We also calculated the acceleration $$a$$ to be $$1.25 \, \mathrm{m/s^2}$$.
Using all these variables, we get $$s = 2.5*2 + \frac{1}{2}*1.25*2^2$$. That is, $$s = 5 + \frac{1}{2}*1.25*4$$. So, $$s = 7.5 \, \mathrm{m}$$.