#### Answer

$y'' = 24t - 18$
$y''' = 24$

#### Work Step by Step

To calculate $y''$, first we must find $y'$ using the power rule:
$y' = 3*4t^2 - 2*9t = 12t^2 - 18t$
Now, $y''$ is the derivative of $y'$, which we can once again find using the power rule:
$y'' = 2*12t - 18 = 24t - 18$
To calculate $y'''$, we take the derivative of $y''$ with the power rule:
$y''' = 24$