Each inch equals exactly 2.54 cm Each penny is 3/4 of 2.54 cm or .75x2.54=1.905 cm
one km = 1,000 meters. each meter = 100 centimeters
one km =1000x100 = 1 with five zeros or 100000 cm
8 km = 800000 cm Divide 800,000 cm by 1.905 cm to get the number of pennies needed
419,947.5 so you need 419,948 pennies, although that's slightly longer than need, but 1 penny less and it wouldn't be enough.