Via the half-life equation we have:
[tex]A_{final}=A_{initial}(\frac{1}{2})^{\frac{t}{h} }[/tex]
Where A is the amount initially and final amount after some time has passed, t is the time elapsed, h is the half life time and so:
[tex]A_{final}=45(\frac{1}{2})^\frac{140}{35} = 2.8125g[/tex]
Therefore there will be 2.8125 grams left after 140 seconds.
