Pls assistance.you will acquire 10 points.? i have 3 sets of uniform and wear it regularly but ...

i have 3 sets of uniform and wear it regularly but the cloth undcer my arms remains wan because of sweat.how much ever i try it stays yellow and adjectives my uniforms are alike.
Many of the people contained by my class also have thias problem.pls lend a hand.what to do?
Answers:    You can use Iron out on your clothes. My boyfriend has done this to his white clothes and it worked.
Try wipe up and rubbing it with or soak it next to white vinegar and water, if that does not work try by carb soda and sea.