Cosine angle B (geometry, right triangles- giving brainliest and thanks to all!)

Samantha swam upstream for some distance in one hour. she then swam downstream the same river for the same distance in only 12 minutes. if the river flows at 4 mph, how fast can samantha swim in still water?

Write the expression in simplified radical form. show all steps and work including any foil method work. (hint: use the conjugate. no decimal answers.) (9-2√3)/(12+√3)

Hi, can anyone show me how to do this problem? 100 points for this. in advance