Chapter P, Prerequisites - Section P.9 - Modeling with Equations - P.9 Exercises - Page 71: 40

$330$ feet by $66$ feet.

The equation for this problem is $(x)(5x)=\frac{43,560}{2}$, where $x$ is the width of the building lot. The equation yields to $x=\sqrt \frac{43,560}{2\times 5}=\sqrt {4,356}=66$ feet. After this, the length is simply $(66)(5)=330$ feet.