If nation x decides to build 900 miles of highways, how many aircraft carriers can it built

Building a 4 lane highway costs between $4,000,000 and $10,000,000 per mile depending on where it runs (rural, suburban or urban areas). So the country has at least (900 * $4,000,000 =) $2,800,000,000 and at most (900 * $10,000,000 =) $9,000,000,000 available for construction. An aircraft carrier costs about $13,000,000,000, so the country would not be able to afford an aircraft carrier instead of the 900 miles of highways.