Let the number of people summoned be n:

$$ Summoned\ people \ who \ appear =40\%n=0.4n $$

$$ Excused\ people =\frac{1}{3}(0.4n) $$

Then,

$$ Jury\ pool =\frac{2}{3}(0.4n) $$

Jury pool should be 60. So

$$ \frac{2}{3}(0.4n)=60 $$

$$ n=\frac{3\times 60\times 10}{2(0.4)} $$

$$ n=225 $$

So choice D is correct.