Five runners together complete a $100$-mile endurance race by running separate, non-overlapping portions of the course.  Runner B's portion is $1.5$ times the length of Runner A's portion.  The combined portion for Runners C and D is twice the length of the combined portion for Runners A and B.  Runner E then runs the last $10$ miles of the race.  How many miles did Runner B run?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Five runners together complete a $100$-mile endurance race by running separate, non-overlapping portions of the course.  Runner B's portion is $1.5$ times the length of Runner A's portion.  The combined portion for Runners C and D is twice the length of the combined portion for Runners A and B.  Runner E then runs the last $10$ miles of the race.  How many miles did Runner B run?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
18
Five runners together complete a $100$-mile endurance race by running separate, non-overlapping portions of the course.  Runner B's portion is $1.5$ times the length of Runner A's portion.  The combined portion for Runners C and D is twice the length of the combined portion for Runners A and B.  Runner E then runs the last $10$ miles of the race.  How many miles did Runner B run?
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