Mark rides his bike from his house to the closest edge of the park, across the length of the park, and then back home. The distance from his house to the closest edge of the park is 0.9 km and the distance from the far side of the park to his house is 1.6 km. The map shows the path Mark took on his bike. If ∠B = 85° on the map, then use the law of cosines to determine the length of the park in kilometers.