The length and width of the workspace at the bottom edge of the window is 18 inches and 52 inches. What is the correct grid spacing for downflow velocity measurement per NSF/ANSI 49? a. 6.0 inches x 6.7 inches. b. 6.0 inches x 5.7 inches. c. 3.0 inches x 5.7 inches d. 3.0 inches x 6.0 inches. e. 6.0 inches x 6.0 inches.