Answer:
 16,900 ft²
Step-by-step explanation:
The area of a rectangle is the product of length and width.
The area of the lot is ...
 (150 ft)(250 ft) = 37,500 ft²
The area of the driveway is ...
 (20 ft)(30 ft) = 600 ft²
The area of the lot not used for house or driveway is ...
 grass area = 37,500 ft² -20,000 ft² -600 ft² = 16,900 ft²