Question

if $c = x + 6$ and $d = 3x - 6 + 4x^2$, find an expression that equals $c + 3d$ in standard form.

Explanation:

Step1: Substitute D into 3D

$3D = 3(3x - 6 + 4x^2)$

Step2: Expand 3D

$3D = 9x - 18 + 12x^2$

Step3: Add C to 3D

$C + 3D = (x + 6) + (9x - 18 + 12x^2)$

Step4: Combine like terms

$C + 3D = 12x^2 + (x + 9x) + (6 - 18)$

Step5: Simplify the expression

$C + 3D = 12x^2 + 10x - 12$

Answer:

$12x^2 + 10x - 12$