A window is made of a rectangle 84 cm wide and 100 cm tall with a semicircular top of the same width fitted above it. What is the total area of glass in the window, in square cm? (Use π = 22/7.)

The rectangle gives $84\times 100=8400$ sq cm. The semicircle spans the 84 cm width, so its radius is 42 cm and its area = $(1/2)\times (22/7)\times 42^2=(1/2)\times 5544=2772$ sq cm. Total = 8400 + 2772 = 11172 sq cm. The trap 13944 adds a whole circle instead of a half; 19488 takes the width 84 cm as the radius; 8400 counts only the rectangular pane.