Q$3/$Using the following button $,$ and find a solution for this question $.$

This is the last number of your phone number.

$(0\mathrm{.}5a-2\}$

$\frac{1}{x}1+0\mathrm{.}0\frac{a}{x}20\mathrm{.}35a+10$

$x11$

$x21\mathrm{.}5$