Product of Complex Numbers

Consider the complex numbers:

$z_1 = 3 + 4i$

and

$z_2 = 1 - 2i$.

Calculate the product of these two complex numbers: $z_1 z_2$. Express your answer in the form $a + bi$, where $a$ and $b$ are real numbers. Enter the real part $a$ followed by the imaginary part $b$ of your answer, separated by a space.