1) when a spring is stretched, its length increases from 58 cm to 66 cm. calculate its extension.
2) your friend has fallen through the thin ice on a frozen pond. you come to the rescue by laying a ladder across the ice and crawling along the ladder to reach your friend. use the idea of pressure to explain why it is safer to use the ladder than to walk on the ice.

1) 8 cm    

2) Using the ladder is safer.

Explanation:

1) 66 cm - 58 cm= 8 cm

It is important to understand what is meant by 66 cm and 58 cm in the given sum. It says the length of the spring has been increased from 58 cm to 66 cm while stretching which suggest the initial length of the spring is 58 cm and final length the spring attain after stretching is 66 cm. You know that (final length) - (initial length) = extension.

2) Pressure = (Magnitude of the force)/ (area normal to the force)

A thin fragile layer of ice may not be able to bear the pressure created by your feet on it and will crack from the weakest point. Like a pin can pierce through wood by force of your thumb. But what if you decrease the pressure, like using your thumb to pierce the same piece of wood? Its not very likely to happen. The difference between the pin and the thumb is the surface area which the force is acting. So you will use a ladder which can be laid on the pond to increase the surface area which decrease the pressure created by your weight  (and your friend's when rescued) to make sure no more ice is going to be cracked!