Khan Academy Passage question- ECG + Fourier Transform

I am enjoying this Khan Academy stuff but holy fish paste this question makes 0.000% sense to me.

Question talks about how you can transform a function with two sine graphs using fourier transform to an ECG-like reading on question 3 of the passage. You should be able to see it here:
https://www.khanacademy.org/test-prep/mcat/physical-sciences-practice/physical-sciences-practice-tut/e/analyzing-electrocardiogram-voltage-signals

How do I tackle this kind of problem??