Mrs. Tilmos creates a new garden in her yard in the shape of a triangle. One side of the garden measures 13 feet and is perpendicular to a second side which is twice as long. Before she plants her flowers, she wants to mix a fertilizer into the soil, whose directions say to use 1 cup per every 20 square feet. How many cups of fertilizer should she use? Enter your answer as a decimal, rounded to the nearest 1/2 cup. ​