Calcula el promedio de cada conjunto de datos.
a) 7, 9, 10, 12, 12, 12, 15
b) 22, 22, 22, 24, 25, 35
c) 6, 8, 8, 8, 10, 12, 13, 15
d) 10, 14, 14, 14, 18, 20