helping nephew with paper. its english from paper, so i type exactly:

1. a particle is moved along the x-axis by a force that measures $\displaystyle \frac{15}{(1+x)^2}$ pounds at a point x feet from the origin. Find the work done in moving the particle from the origin to a distance of 14 feet.

i have no book.

other problem also about work:

1. If 128 J of work are needed to stretch a spring from 8cm to 12cm and another 432 J are needed to stretch it from 12cm to 18 cm. What is natural length of spring?

i am elementary math teacher in italia, so don't remember from college! thanks you everybody!