If $a^3+b^3=405$ and a + b = 9, then the value of ab is

10 15 8 12

12

a3 + b3 = 405 a + b = 9  (a + b)3 = a3 + b3 + 3ab(a + b) = (9)3 = 405 + 3ab (9) = 729 = 405 + 27ab = 27ab = 324 = ab = 12