A 100-acre farm is subdivided into lots for homes.  The streets require one-eighth of the entire property, and the remaining acreage is divided into 140 lots of approximately the same size.  About how many square feet are in each lot?

A lot has a frontage of 140 feet and a depth of 170 feet.  If the building line regulations call for a setback of 30 feet at the front, 10 feet at the back, and 8 feet on each side, how many square feet of usable space are left for the building?