Answer:
x = 9 ⇒ second answer
Explanation:
∵ (a + 3)(-2a² + 15a + 6) =
-2a³ + 15a² + 6a - 6a² + 45a + 18 =
-2a³ + 9a² + 51a + 18
∵ (a + 3)(-2a² + 15a + 6) = -2a³ + xa² + 51a + 18
∴ -2a³ + 9a² + 51a + 18 = -2a³ + xa² + 51a + 18
∴ x = 9
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