Answer:
The 36°30' line, also called the Missouri Compromise line, was a boundary line set up by the Missouri Compromise of 1820. Slavery was not allowed in the territories north of that line, but it was allowed in the territories south of that line. But the 36°30' line only applied to the land that was bought through the Louisiana Purchase and the Northwest Territory. It did not apply to land that was bought through other means, like the Mexican Cession, which gave the United States the land that is now Utah.
So, the 36°30' line would not have applied to Utah, and its position on slavery would have depended on the specific laws passed by the U.S. Congress at the time Utah became a territory or later. As we've already said, Congress passed the Compromise of 1850, which made it possible to have slaves in Utah Territory. However, many Mormons were against slavery, and the economy of the territory was strong enough to support itself without slaves.