76. The greatest gap between rims in the Grand Canyon on a map is $2.9 \mathrm{~cm}$. Determine the actual gap in $\mathrm{km}$, if the scale factor is $1 / 1000000$.

Step 1 ：Given the gap on the map in centimeters: gap_on_map = 2.9 cm

Step 2 ：Given the scale factor: scale_factor = 1 / 1000000

Step 3 ：Calculate the actual gap in kilometers: actual_gap = gap_on_map * scale_factor

Step 4 ：actual_gap = 2.9 * 1e-06

Step 5 ：actual_gap = 2.9e-06 km

Step 6 ：\( \boxed{\text{Final Answer: The actual gap in the Grand Canyon is approximately 2.9 km}} \)