If 2a+3b=12 and ab=6 find the value of 8a^3+27b^3

(2a + 3b)^2 = 4a^2 + 12ab + 9b^2 =
((4a^2 - 6ab + 9b^2) + 18ab) = 144
4a^2 - 6ab + 9b^2 = 144 - 18 ab

8a^3 + 27b^3 = (2a + 3b)(4a^2 - 6ab + 9b^2)
8a^3 + 27b^3 = (2a + 3b)*(144 - 18ab)
8a^3 + 27b^3 = 12 * (144 - 18ab)
= 12 * ( 144 - 18*6) since ab = 6
= 12 * (144 - 108)
= 12 * (36)
=  432 <<<< answer 

The following relation is not a function