The sale amount was analyzed by store location and shelf position.Based on the output table below,how many cells (groups) were in the factorial design?

Tests of Between-Subjects Effects Dependent Variable: Sales Type Ill Sum Source of Squares df Mean Square F Sig. Corrected Model 503.754 100.751 5.397 007 Intercept 6740.928 6740.928 361.121 000 Store 7.014 7.014 .376 550 WNNHHU Shelf 457.568 228.784 12.256 .001 Store * Shelf 30.114 15.057 .807 .467 Error 242.667 18.667 Total 7342.000 19 Corrected Total 746.421 18 a. R Squared = .675 (Adjusted R Squared = .550)