Answer:
(x+9)(3x+27)
Step-by-step explanation:
3x^2+54x+243 (243×3=729, Product=729, Sum=54) [27+27=54, 27×27=729]
3x^2+27x+27x+243
3x(x+9)+27(x+9)
=(x+9)(3x+27)
