Final answer:
To calculate the height of Chrystelle's mother, add the 15 ft to Chrystelle's height of 3 ft, giving a total of 18 ft for the mother's height.
Step-by-step explanation:
The question asks for the height of Chrystelle's mother, knowing that Chrystelle is 3 ft tall and her mother is 15 ft taller than her. To find the mother's height, we simply add 15 ft to Christelle's height:
Chrystelle's height = 3 ft
Mother's additional height = 15 ft
Mother's total height = Christelle's height + Mother's additional height
Mother's total height = 3 ft + 15 ft = 18 ft
Therefore, Chrystelle's mother is 18 ft tall, making the correct answer B. 18 ft.