The first thing you should know is that the distance is equal to the speed per time.
Therefore if You walk forward at 1.5 m / s for 8s
d = 1.5t [0,8] s
Your friend decides to walk faster and starts at 2.0 m / s for the first 4 s.
d = 2t [0,4] s
Then she slows down and walks forward at 1.0 m / s for the next 4s
d = t + 4 [4,8] s
Who walked farther?
They both walked the same distance
12 meters
Therefore if You walk forward at 1.5 m / s for 8s
d = 1.5t [0,8] s
Your friend decides to walk faster and starts at 2.0 m / s for the first 4 s.
d = 2t [0,4] s
Then she slows down and walks forward at 1.0 m / s for the next 4s
d = t + 4 [4,8] s
Who walked farther?
They both walked the same distance
12 meters