Find the missing numbers $(A,B)$ in the series and find the value of $B+A$.
$$25,36,49,A,81,B,121$$

1. Let's look at the pattern of the numbers in the series:
* $25=5^2$
* $36=6^2$
* $49=7^2$
* $A=8^2=64$
* $81=9^2$
* $B=10^2=100$
* $121=11^2$

2. Thus, the series consists of squares of consecutive natural numbers starting from $5$.
3. We have found:
* $A=64$
* $B=100$

4. Now, calculate the required value $B+A$:

$$B+A=100+64=164$$