Help! Please Can you tell me how you do this? Thank you!

I'm confused on this could anyone me and show me what i need to do to solve it.

If two lines form congruent alternate interior angles with a transversal, then the lines

Right triangle abc has three sides with lengths ab= 119, bc = 169, ca= 120. find the value of cos c. hint: draw and label the triangle. the hypotenuse is always the longest.