Now, speed is distance over time while velocity is displacement over time. Since we’re talking about the same object’s motion, the total time traveled is (120 + 90) = 210 seconds.
Now, the total distance traveled by the object is (400 + 250) = 650 m. Meanwhile the total displacement traveled by the object is 400 m, East + 250 m, West = 150 m, East.
Now, to find the speed and velocity, we just divide the values of distance and displacement, respectively, over time. Thus, we have
speed = 650 m / 210s ≈ 3.095 m/s
velocity = 150 m, East /210 s ≈ 0.714 m/s, East
Now, rounding the values up to 2 significant digits, we have
a) speed = 3.1 m/s
b) velocity = 0.71 m/s, East