first lets add the 2 distances on the map:
3 3/4 + 5 1/4 = 9 inches ( 3/4 + 1/4 = 1, 3+5 = 8, 8+1 = 9 )
1/2 inch on the map = 4 miles
there are 2 1/2 inches to 1 inch so 4 miles x 2 = 8 miles to 1 inch
so now multiply 9 inches x 8 miles = 72 total miles