$$\left({\mathtt{80}}{\mathtt{\,\times\,}}{\mathtt{80}}\right){\mathtt{\,\times\,}}{\mathtt{4}}{\mathtt{\,\times\,}}{\mathtt{4}}{\mathtt{\,-\,}}{\frac{{\frac{\left({\mathtt{893}}{\mathtt{\,\times\,}}{\mathtt{893}}\right)}{{\mathtt{4}}}}}{{\mathtt{16}}}} = {\mathtt{89\,939.859\: \!375}}$$