A buffer solution with a pH of $4\mathrm{.}0$ is made by dissolving $xg$ of potassium ethanoate $(C_{?}{H}_3$COO $K)$ in a solution of ethanoic acid $(C{H}_3$COO $H).$ The final volume of the buffer solution is $500c{m}^3$ and the final concentration of the ethanoic acid is $0\mathrm{.}250mold{m}^{-3}.$ Calculate $x$ in $g$ for potassium ethanoate, the concentration of H$+$ ions where the answer is $\_\_\_\_$x$10^4$ moldm$-3,$ the concentration of CH$3$COO$-$ where the answer is $\_\_\_$x$10^2$ moldm$-3.$ Given

$K_a=1\mathrm{.}74{10}^{-5}mold{m}^{-3}$