A rectangular field with a perimeter of 42 feet must have an area of at least 104 square feet (or possibly more). What are the possible values for the length of one side so that both conditions are met? Express your answer in interval notation.

Note: If the answer includes more than one interval write the intervals separated by the "union" symbol, U. If needed enter $\infty$ as infinity and $-\infty$ as -infinity .