Answer:
Acceleration is the change in velocity over the change in time = Δv/Δt. To do these problems, you need to find out how much the speed changed and over what period of time it changed.
Snail 1 changes from 4 cm/min to 7 cm/min in 3 minutes. Subtract the starting velocity (4 cm/min) from the ending velocity (7 cm/min) then divide by the time (3 min):
Snail 1 = (7 cm/min. - 4 cm/min)/(3 minutes) = ? (remember to put down the units)
Snail 2 changed from 7 cm/min. down to 1 cm/min. in 3 minutes
Snail 2 = (1 cm/min. - 7 cm/min.)/(3 min.) = ? (note that the acceleration is negative when you slow down)
I hope this helps you