How to simplify 8/13 - 25/13 into mixed number fraction?

Need solving this second acceleration problem.

If sr is 4.5cm and tr is 3cm, what is the measure in degrees of angle s?

Abag contains 4 red, 7 blue and 5 yellow marbles. event a is defined as drawing a yellow marble on the first draw and event b is defined as drawing a blue marble on the second draw. if two marbles are drawn from the bag, one after the other and not replaced, what is p(b|a) expressed in simplest form? a. 7/16 b. 7/15 c. 14/16 d. 14/15