It is given that
Losing candidate got 42% of the votes polled
Votes secured by winning candidate = $$\left (100 - 42 \right )$$ % of the votes polled = 58 % of the votes polled
So the difference of votes $$= 58\% - 42\%$$
= 16% of the votes polled
We know that
16% of the votes polled $$= 14400$$
16%/100 of the votes polled $$= 14400$$
So the votes polled = $$14400 \times 100/16$$
By further calculation
$$= 900 \times 100$$
$$= 90000$$
Here
Total number of eligible voters $$= 100000$$
No. of voters who did not vote $$= 100000 - 90000$$
$$= 10000$$
Percentage of voters did not vote = $$\left [10000 / 100000 \times 100 \right ]$$ %
By further calculation
$$= 10000/1000$$ %
$$= 10$$ %