Chapter 11.3, Problem 11.3CE

When two objects collide, the impulse exerted on object 1 by object 2 is equal in magnitude and opposite and direction to the impulse exerted on object 2 by object 1:

${\stackrel{\to }{I}}_{[1\text{ on 2}]}=-{\stackrel{\to }{I}}_{[2\text{ on 1}]}$    (11.8)

And the change in their momenta is given by:

$\Delta {\stackrel{\to }{p}}_1=-\Delta {\stackrel{\to }{p}}_2$    (11.9)

Which of Newton’s three laws justifies these two equations?