Step 1: Find the add of the real parts.
$$ 4+6 = 10 $$Step 2: Find the add of the imaginary parts.
$$ 18i+8i = 26 i$$Putting all together we have:
$$ \begin{aligned} z_1 + z_2 & = \left( 4+18i \right) + \left( 6+8i \right) = \\ & = \left( 4+6 \right) + \left( 18i+8i \right) = \\ & = 10+26i \end{aligned} $$