Mary is x years old. How old will she be in 9 years? How old was she 8 years ago
In 9 years, we add, since her age goes up, so she'll be:
x + 9
8 years ago, we subtract, since her age goes down, so she'll be:
x - 8
In 9 years, we add, since her age goes up, so she'll be:
x + 9
8 years ago, we subtract, since her age goes down, so she'll be:
x - 8