Answer:
x = 10
Step-by-step explanation:
3x - 9 = 21
add 9 on both sides:
⇒ 3x - 9 + 9 = 21 + 9
⇒ 3x = 30
divide 3 on both sides:
⇒ 
⇒ x = 10
to check answer, substitute x by 10 on the original equation:
⇒ 3x - 9 = 21
⇒ 3 x 10 - 9 = 21
⇒30 - 9 = 21
⇒ 21 = 21
The expression that represents the volume would be: <span>C) 6x^3+39x^2+54x</span>
Proof of the calculation:
V = Lwh
V = (x+2) (3x) (2x+9)
V= (3x^2 + 6x) (2x + 9)
V = (6x^3 + 27X^2 +12x^2 + 54x)
V = 6x^3 + 39x^2 + 54x