First, since the snake is travelling at a constant velocity, find out how long it takes the snake to go 45m (you have a 5m head start).
<span><span><span>45m</span><span>1.5m/s</span></span>=30s</span>
Now you just need to go your 40 meters in that amount of time:
<span>Xf−Xi=1/2(Vi+Vf)t</span>
<span>40m−0m=1/2(0+Vf)(30s)</span><span><span><span>40m∗2</span><span>30s</span></span>=Vf=2<span>23</span>m/s</span> Since you're starting from rest, your average speed must be half of that which is <span>1<span>13</span>m/s</span>
So at 40m, you and the snake will be at the same point however you will be going <span>2<span>23</span>m/s</span> at that point so the snake cannot overtake you.
Looking back at the question, I believe it wants to know what your average speed needs to be...which is:<span><span>>1<span>13</span>m/s</span></span>