if the length of JK is 16.4 miles, it will be diameter of this circle, the radius will be JK/2 = 8.2 miles
As we know the length of circle is 2π*r in this case r = 8.2
The arc JM is 1/4 length of the whole circle so arc JM = (2π*8.2)*(1/4) = 2π*8.2/4 = π*8.2/2 = π*4.1
if we assume that π=3.14 the answer will be 3.14 * 4.1 = 12.874.... And as the answer needs to be rounded to the nearest tenth it will be 12.874≈12.9
So the answer will be 12.9