Explain what percentage of the parent element will decay into the daughter element through the process of radioactive decay during each of the first 3 half lives?

They are called half lives because half the mother isotope decays down to the daughter isotope during each half life. So, during the first one, 50% will decay. During the second, another 50% of the remaining 50% decays. During the third, 50% of the 50% of the 50% will decay.