By 1860 the number of miles of railroad tracks throughout the United States had risen to

By 1860, 30,000 miles (49,000 km) of railroad tracks had been laid,.

By 1860, 30,000 miles (49,000 km) of railroad tracks had been laid, with 21,300 miles (34,000 km) concentrated in the northeast.

b)

it created free trade throughout the colonial territories.

hello there!

the graphics that you have attached within the question, indicates that few people in bolivia work in industry according to its labor force.

however, the graphic that is on the right side of the picture shows the gdp sector in bolivia. this gross domestic product is a macroeconomic magnitude   that shows the monetary value of all finished goods and services within a country's borders in a specific time period. in this case, the graphic is showing the monetary value in each sector -agriculture, industry and services- of bolivia in 2012.

so, although the first graphic located at the left side indicates that not so many people work in industry, this is the second most important sector according to the gdp metrics because of the monetary value that impacts on its country. it does not need to be the most valuable one. if it makes an impact on the country's economy, it will be definitely crucial to it.