We know that the mgf corresponds to only one probability function. Therefore we want to find the form of the mgf in question. Looking up in tables or by memory, we identify a form similar to the one of an exponential mgf:
$$
M_x(t)=\frac{1}{1-\theta t}
$$
For an exponential of the form
$$
\frac{1}{\theta}e^{-(1/\theta )x}
$$
Also we can assume that the behavior of the components is independent from each other, so the product of the moment generating functions is the joint moment generating function. Solving a simple equation:
$$
\frac{1}{(1-\theta_1 t)}\frac{1}{(1-\theta_2 t)}=\frac{1}{1-3s-2t-6ts}
$$
Giving that $\theta_1=2$ and $\theta_2 = 3$. Therefore we want to calculate the probability of either component $X$ or $Y$ lasting less than some time $k$. Therefore we want to consider the minimum of either of the distributions failing before time $k$. We also know that $\min\{X_i\}$ when those $X_i$ are exponentials, the new minimum random variable has a distribution of the products, which should be easy to follow from here.
Just in case, The distribution of the minimum of the exponentials is an exponential with the parameter $\lambda_{min}=\sum \lambda_i$, where $\lambda_i=\frac{1}{\theta_i}$ because we used the alternative parametrization of the exponential in the problem.