This is a word problem so translate to math so this is asking 6+(4/2) which is 8
About 102.5625... I think
We know that
<span>1 1/8 gallons----------> (1*8+1)/8-------> 9/8 gallons
</span><span>13 1/2 miles----------> (13*2+1)/2-------> 27/2 miles
if 9/8 gallons-------------------> 27/2 miles
1 gallons----------------------> X
X=(27/2)/(9/8)---------> 216/18--------> 12 miles
the answer is 12 miles</span>
For any equation,

assume solution of a form, 
Which leads to,

Simplify to,

Then find solutions,

For non repeated real root y, we have a form of,

Following up,
For two non repeated complex roots
where,

and,
the general solution has a form of,

Or in this case,

Now we just refine and get,

Hope this helps.
r3t40
The answer is B! Good luck!