The innovation of the steamboat significantly contributed to the growth of the U.S. economy primarily through option d: prices of fares and cost to transport goods decreased.
Steamboats allowed for faster and more efficient transportation of goods and people along rivers, which reduced shipping costs and transit times. This efficiency helped stimulate trade, opened up new markets, and facilitated westward expansion, thereby boosting the overall economy. While the other options may have some indirect connections to the effects of steamboats, the most direct impact on the economy relates to the decrease in transport costs.