Final answer:
By applying the conversion factor of 1.61 kilometers per mile, the 8-mile long marathon is equivalent to 12.88 kilometers.
Step-by-step explanation:
To find out how long the marathon was in kilometers (km), we need to use the conversion factor between miles and kilometers. We have been provided with the conversion rate of 1 mile being equivalent to 1.61 km. The marathon was 8 miles long, and by multiplying this distance by the conversion factor, we can obtain the length of the marathon in kilometers.
To calculate: 8 miles × 1.61 km/mile = 12.88 km.
Therefore, the marathon was 12.88 kilometers long.