So, we've been doing these lately in my intro to calc class, and I'm not getting them at all, I get normal displacement and stuff but when it comes to relating it to a word problem they make me

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When a person is breathing normally, the amount of air in their lungs varies sinusoidally. When full, Karen's lungs hold 2.8 liters of air. When empty, her lungs hold 0.6 liters of air. Her brother starts timing her breathing. At t = 2 seconds she has exhaled completely and at t = 5 seconds she has inhaled completely. Find an EQ that will model the amount of air in Karen's lungs at any time, assuming she breathes normally.

All I know, or want to assume, is that in 3 seconds she exhale and inhales, that's all I understand..