For number 15, each side would be 2 miles long. 6/3 is 2. This is a whole number and the rougher would be an equilateral triangle.
The answer is 2 miles
For number 16, you must use the Pythagorean theorem
A squared + b squared = c squared
5 squared + 12 squared = c squared
25+144= c squared
169= c squared
The square root of 169 is 13
The answer is 13 feet