The speed of the snail is given by:

where S is the distance covered by the snail and t the time taken.
The snail in the problem moves by S=18 mm in t=24 s, therefore its speed is

Answer:
Input impedance of this transformer is 50 ohms.
Explanation:
Given that,
Number of turns in the primary coil, 
Number of turns in the secondary coil, 
Output impedance of the transformer, 
The number of turns and the impedance ratio in the step down transformer is given by :

So, the input impedance of this transformer is 50 ohms. Hence, this is the required solution.