B, good luck, hope this helps :)
ANSWER:
250 J
STEP-BY-STEP EXPLANATION:
F = 20N is required to stretch the spring by 4 meters
We know that the force is equal to:

We solve for k (spring constant):

The work done in stretching the spring is given by the following equation (in this case the stretch is 10 meters:

The work required is 250 joules.
Answer:

Explanation:
We are going to use the accelerated motion formula
on the vertical component taking the upwards direction as positive.
Since <em>at maximum height the speed will be
</em>, the formula can be written as
, which for our values is:

Written to three decimal places.