Sandra is riding a bicycle at 10.0 meters/seconds. SHe slows down to 2.0 meters/seconds in 10 seconds. Her acceleration is. how many meeters / seconds?

Answer: a = - 0.8 m/s2 distance = x = 60m

Explanation: vo=10m/s, vf=2m/s, t=10s

a = (vf-vo) / t = (2-10) / 10 = - 0.8 m/s2 (sign means reduce your seed)

the second question is not clear. i do believe that you need the distance sandra moved (units ... meters ... not meters/second)

x=xo + vot + at*t/2 = 0+10*10-0.8*10*10/2 = 60m

best wishes form colombia