After 49 years you'll have
What you've essentially have to perform is a nuclear half-life calculation starting from the initial ratio of tritium to hydrogen atoms.
In tritium's case, the total number of atoms will be reduced to half after every half-life; this means that you'll have half of the number of tritium atoms after 12.3 years, a quarter of the initial tritium atoms after 2 * 12.3 = 24.6 years, and so on.
Since normal hydrogen is considered stable, i.e. it has a half-life that's bigger than the age of the universe (by a lot), the number of hydrogen atoms will remain the same.
You can use the nuclear half-life equation to see how many tritium atoms you'll have after 49 years
So, plug your data into this equation and solve for
Rounded to 1 sig fig, the number of sig figs in