Need help on permutation question. A child has plastic toys: 3 pyramids, 4 cubes, and 7 spheres.?

In how many ways can you select 3 objects, one of each shape, if the order in which the objects are selected does not matter, and each object is a different color? Back of my book says 84 but i can't figure out how they go that number. I really don't understand the more complicated permutations. The simple ones like organizing 7 cd's on a shelf are easy enough, but not these.