As part of a history project, four students are making a 12-foot-tall model of a pyramid. The four faces of the pyramid will be congruent triangles. Each face will be given to a different student in the group to add texture and paint. The student working on the back face of the pyramid takes some measurements and determines that he will need enough material to cover 84 square feet. How much material will the student working on the left face need to cover her side of the pyramid?