The ratio of the number of atoms of two radioactive elements A and B, in equilibrium with each other, is `3.1 xx 10^(9): 1`. If `t_((1)/(2))` of element B is 6.45 yrs, calculate that of element A.

Explanation

To solve the problem, we need to find the half-life of element A given the ratio of the number of atoms of elements A and B in equilibrium and the half-life of element B.

### Step-by-Step Solution:

1. **Understand the Given Ratio**:
The ratio of the number of atoms of elements A and B in equilibrium is given as:
\[
\frac{N_A}{N_B} = 3.1 \times 10^9 : 1
...