If (2 − 3i) + (x + yi) = 6, to get x + yi we subtract (2-3i) from both sides of the equation.
(2 − 3i) + (x + yi) - (2 − 3i) = 6 -(2 − 3i)
(x + yi) = 6 - (2 - 3i)
Open the parenthesis taking care of the signs
(x + yi) = 6 - (2 - 3i)
= 6 - 2 + 3i
= 4 + 3i