Answer
$12000\leq m\leq 14000$
Work Step by Step
To determine the corresponding range of miles we have to take $2$ key point, these are maximum and minimum amount of budget ($6400\$$ and $7100\$$).
$6400=0.35m+2200$
$0.35m=4200$
$m=12000$
$7100=0.35m+2200$
$0.35m=4900$
$m=14000$
We got the following range:
$12000\leq m\leq 14000$
