$X + Y$ one day work $= \frac{1}{8}$ $-(i)$
$\frac{X}{2} + 2Y$ one day work $= \frac{1}{5}$
$X+4Y$ one day work $= \frac{2}{5}$ $-(ii)$
$4 \times (i) - (ii)$
$3X$$= \frac{1}{2} - \frac{2}{5}$
$X$ one day work $\frac{1}{30}$
Total days taken by $X = \color{Red}{30}$
