Question 32931
Let the unknown distance be "x".
Nine Thousand mph rocket data:
distance = x; rate=9000mph;  time= (x/9000)hrs.
Ten Thousand mph rocket data:
distance = x; rate=10000mph; time= (x/10000)hrs.
EQUATION:
 time-time= (1/4)hr.
x/10000 -x/9000 = 1/4
[9000x-10000x)/(9E7)=1/4
 1000x=9E7/4
x= 9E7/4000
x= 22500 miles
Cheers,
Stan H.