Final answer:
The height of the tree at the end of 6 years will be 120 cm.
Step-by-step explanation:
To find the height of the tree at the end of 6 years, we can calculate the growth rate per year. Since the tree grew 10 cm in ½ of a year, it means it grows at a rate of 20 cm per year. To find the height after 6 years, we can multiply the growth rate by the number of years: 20 cm/year x 6 years = 120 cm. Therefore, the height of the tree at the end of 6 years will be 120 cm (option b).