In order to calculate how much square feet he will be able to cover, we can use the following rule of three:
[tex]\begin{gathered} \text{ number of bags}\to\text{ square feet covered} \\ 1\text{ bag}\to235.5\text{ ft2} \\ 2\text{ 3/4 bags}\to x\text{ ft2} \\ \\ \frac{1}{2\frac{3}{4}}=\frac{235.5}{x} \\ x=235.5\cdot2\frac{3}{4} \\ x=235.5\cdot(2+\frac{3}{4}) \\ x=235.5\cdot(\frac{8}{4}+\frac{3}{4}) \\ x=235.5\cdot\frac{11}{4} \\ x=647.625 \end{gathered}[/tex]Erin will be able to cover 647.625 ft².