Answer:
6 a³ + 25 a ² b + 12 a b ² - 7 b³
Explanation:
First, you have to simplify like (a + b) x (3 a - b) x (2 a + 7 b)
Second, you have to collect like terms like (3 a² + 2ab - b²) x (2 a + 7 b)
You have to simplify again after that like (3 a ² + 2 a b - b ²) x (2a + 7b)
Collect like terms again like 6 a ³ + 21 a² b + 4 a ² b + 14 a b ² - 2 a b² - 7 b³
After all that, the solution is 6 a³ + 25 a ² b + 12 a b² - 7 b³
Hope this helps!