A quick way to solve nuclear half-life problems is by remembering that, esentially, you are dividing whatever amount you have by 2 for every half-life.
So, if you start with, say, 100 g of a radioactive isotope that has a half-life of 1 million years, you will have
So, for this example, you are left with 1/4th of the original sample after 2 "cycles". Therefore, since, in your case, the element's half-life is 703 million, 2 "cycles" mean
703 + 703 = 1406 million = 1.4 billion years.
If the problem would have asked for, say, 1/16th of the original sample, that would have corresponded to