First, expand
(2x + 3)² = (2x + 3)(2x + 3)
Use the FOIL method (First, Outside, Inside, Last)
(2x)(2x) = 4x²
(2x)(3) = 6x
(3)(2x) = 6x
(3)(3) = 9
4x² + 6x + 6x + 9
Combine like terms
4x² (+6x + 6x) + 9
4x² + 12x + 9
4x² + 12x + 9 is your answer
hope this helps