Respuesta :
Answer:
r is radius and the mm are milimeters
Step-by-step explanation:
A circle of radius = 13 or diameter = 26 or circumference = 81.68 mm has an area of: 5.309 × 10-10 square kilometers (km²) 0.0005309 square meters (m²) 5.309 square centimeters (cm²)