A mixture of 1.00 mol of ethanoic acid and 3.00 mol of ethanol is heated with a little concentrated…

Step 1. $4 = \dfrac{x^2}{(1 - x)(3 - x)}$ gives $3x^2 - 16x + 12 = 0$.

Step 2. $x = \dfrac{16 - \sqrt{256 - 144}}{6} = \dfrac{16 - 10.58}{6} = 0.903$, which is $90.3\ \%$.

Step 3. Mass $= 0.903\ \text{mol} \times 88.11\ \text{g/mol} = 79.5\ \text{g}$.

What would raise the yield? More ethanol, or removing the water as it forms. Neither changes $K$, but each moves the balance towards the ester.