次の計算をし，ア～カに当てはまる数や数式を半角英数字で入力しなさい。

1. ${\displaystyle \frac{1}{2}{x}^{2}y÷(-x)\times 4y=\boxed{\text{ア}}x{y}^{\boxed{\text{イ}}}}$
2. ${\displaystyle (x^{2}y{)}^2÷(x^4{y}^3)\times (-x{y}^2)=\boxed{\text{ウ}}}$
3. ${\displaystyle 3b^2\times (-2ab{)}^2÷4a{b}^3=\boxed{\text{エ}}}$
4. ${\displaystyle -2x^2÷(-\frac{3}{2}{x}^3{y}^2)\times {(-\frac{3}{4}xy)}^2=\frac{\boxed{\text{オ}}}{\boxed{\text{カ}}}}$