Emma's sister is 7 + 9 = 16 years old. In this many years, Emma's sister will be 56 years old: 56 - 16 = 40 years. When her sister is 56 years old, Emma will be 7 + 40 = 47 years.
This justifies what answer for what question? Q & A:
Emma is 7 years old. If her sister is 9 years older than her, how old will Emma be when her sister is 56?
47