Question 31480
The problem is really asking:
What is the difference in the radii of two circles, one having a circumference (C1) of 25,000 miles and the other having a circumference (C2) of 25,000 miles + 18 feet.

The circumference (C) of a circle, in terms of the radius (r), is given by:
{{{C = 2(pi)r}}} Rewrite this in terms of r.
{{{r = C/2(pi)}}}

For the first circumference (C1=25,000 miles), we can write:

{{{r1 = C1/2(pi)}}}
For the expanded circumference (C2=25,000 mi + 18 ft) we can write:
{{{r2 = C2/2(pi)}}}

To find the difference (d), we'll subtract r1 from r2.
{{{d = C2/2(pi) - C1/2(pi)}}}
{{{d = (C2-C1)/2(pi)}}}
But {{{C2-C1 = 18}}}feet
So:
{{{d = 18/2(pi)}}}
{{{d = 9/(pi)}}}
{{{d = 2.865}}}Feet.