In a race, a runner traveled 12 meters in 4.0 seconds as she accelerated uniformly from rest. the magnitude of the acceleration of the runner was

The runner is moving by uniformly accelerated motion, starting from rest (so, his initial velocity is zero). The law of motion of the runner is

where x(t) is the distance covered after time t, and a is the acceleration of the runner. By re-arranging the formula, we get

We know the runner has covered a distance of S=12m in t=4.0 s, and if we plug these numbers into the equation, we find the acceleration of the runner: 

The low lands i believe