Let's start from this equation:
s = vt + s0
Know what it is? Of course you do. It's the equation used for knowing the position of an object in a certain period of time t.
s is space, v is speed, t is time, s0 is the initial space.
In this case the initial space is equal to 0 so our equation will become:
s = vt
Let's find t:
t = s/v
So:
t = 25m/20m/s = 1,25 s
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Hope it was helpful. Have a great day!