Let the number of people summoned be n:

$$Summonedpeoplewhoappear=40\mathrm{\%}n=0.4n$$

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

Then,

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

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.