JEE Advanced 2020 Paper 1

92238U is known to undergo radioactive decay to form ‌82206Pb by emitting alpha andbeta particles. A rock initially contained 68×10−6g of ‌92238U. If the number of alpha particles that itwould emit during its radioactive decay of ‌92238U to ‌82206Pb in three half-lives is Z×1018, then what is the value of Z?