Answer
There will be a time $t$ when $R_A = R_B$
Work Step by Step
We can write an expression for the decay rate:
$R = R_0~e^{-\lambda t} = \frac{R_0}{e^{\lambda t}}$
The decay rate $R_A$ at $t=0$ is equal to the decay rate $R_B$ at $t = 30~min$
Then, initially, $R_B \gt R_A$ since a decay rate decreases over time.
However, since $\lambda_B \gt \lambda_A$, as time increases, $R_B$ decreases more steeply than $R_A$.
Therefore, there will be a time $t$ when $R_A = R_B$
