Final answer:
To determine the age of Rebecca's mother when Rebecca was born, we subtract Rebecca's current age (15 years) from her mother's current age (43 years), which reveals that her mother was 28 years old at the time of Rebecca's birth.
Step-by-step explanation:
The question asks us to calculate the age of Rebecca's mother when Rebecca was born. To answer this, we need to subtract Rebecca's current age from her mother's current age.
Rebecca is fifteen years old and her mother is 43 years old now.
To find out how old Rebecca's mother was when Rebecca was born, we perform the following calculation:
Mother's age when Rebecca was born = Mother's current age - Rebecca's current age
Mother's age when Rebecca was born = 43 years - 15 years = 28 years old.
Therefore, Rebecca's mother was 28 years old when Rebecca was born.