Mr. Tanabe stood on the middle rung of his ladder to wash windows of an office building. He stepped up 3 rungs to reach more of the windows. Then he saw a spot he had missed on one of the windows below, so he climbed down 5 rungs. After he cleaned that spot, he climbed up 7 rungs and washed the rest of the windows. After he finished, he climbed the remaining 6 rungs to the top of the building to pick up all his equipment. How many rungs did the ladder have?

Also, please write your answer in R. A.C. E form.