Mary is making six ribbon wands. She can only place 15 yards of ribbon on each wand. SHe already has 10 yards of blue ribbon, 25 yards af star ribbon, 20 yards of white ribbon. How many yards does she need of red ribbon?

Solution:

              15 * 6 = 10 + 25 + 20 + R

             R = 90 - 55 = 35 yards