40
Depends on where you and those 15 acres are located.
23,040 acres.
The University of Texas (at Dallas) has an area of 500 acres.
268,601, including water.
It depends on how large the ranch is. A ranch that is only 100 acres may only have 50 cows; "real" ranches that are over 1000 acres in size will have over 500 cows.
200 acres
25 acres
1500 acres
640 acres
114,500 acres
960 square miles or 614,400 acres.
The state of Texas covers about 172,050,000 acres.