4. Let \( x \) and \( y \) be the cost (in million rubles) of the first and second packages of shares, respectively. According to the conditions of the problem, we have the following system:

$$
\begin{aligned}
& \left\{\begin{array}{c}
1.28(x+y)=7.68 \\
1.28(x+y)=1.4 x+1.2 y
\end{array}\right. \\
& \left\{\begin{array}{c}
x+y=6 \\
2 y=3 x
\end{array}\right.
\end{aligned}
$$

$$
\left\{\begin{array}{l}
x=2.4 \\
y=3.6
\end{array}\right.
$$

Thus, the first package of shares cost 2 million 400 thousand rubles, and the second - 3 million 600 thousand rubles.
Answer: 2 million 400 thousand rubles and 3 million 600 thousand rubles.