Why were farmers able to cut their grain more easily and cheaply after 1834?

Cyrus McCormick was born on February 15, 1809, in the Shenandoah Valley of Virginia. He was the eldest of eight children born to inventor Robert McCormick, Jr. (1780–1846) and Mary Ann "Polly" Hall (1780–1853). As Cyrus' father saw the potential of the design for a mechanical reaper, he applied for a patent to claim it as his own invention. He worked for 28 years on a horse-drawn mechanical reaper to harvest grain; however, he was never able to reproduce a reliable version. Cyrus took up the project. He was aided by Jo Anderson, an enslaved African American on the McCormick plantation at the time. A few machines based on a design of Patrick Bell of Scotland (which had not been patented) were available in the United States in these years. The Bell machine was pushed by horses. The McCormick design was pulled by horses and cut the grain to one side of the team. Cyrus McCormick held one of his first demonstrations of mechanical reaping at the nearby village of Steeles Tavern, Virginia in 1831. He claimed to have developed a final version of the reaper in 18 months. The young McCormick was granted a patent on the reaper on June 21, 1834, two years after having been granted a patent for a self-sharpening plow. However, none were sold, because the machine could not handle varying conditions. The McCormick family also worked together in a blacksmith/metal smelting business. The panic of 1837 almost caused the family to go into bankruptcy when a partner pulled out. In 1839 McCormick started doing more public demonstrations of the reaper, but local farmers still thought the machine was unreliable. He did sell one in 1840, but none for 1841.

the answer is b for brother