Question 761917
Middle side = x
Shortest side = x - 75
Longest side = x + 375
x +(x - 75) + (x + 375) = 3075 miles
               3x + 300 = 3075
                      3x = 2775
                       x = 925 miles.
Middle side   = 925 miles
Shortest side = 850 miles
Longest side  = 1300 miles

Total = 3075 miles.
Hope this helps.
:-)