To determine their total age after 5 years, follow these steps:

1. Current Ages:
Let $M$ be the current age of the mother and $D$ be the current age of the daughter. According to the problem:
$$M+D=40$$

2. Ages After 5 Years:
After 5 years, the mother will be $M+5$ years old, and the daughter will be $D+5$ years old.

3. Calculate Total Age After 5 Years:
$$\text{Total age after 5 years}=(M+5)+(D+5)$$
$$=M+D+10$$

Given $M+D=40$:
$$\text{Total age after 5 years}=40+10=50$$


The total age of the mother and daughter after 5 years will be 50 years.

The correct answer is B. 50 years.