The temperature distribution at a certain input of time in concrete slab during curing is given by $$T = 3x^2 + 3x + 16$$ where x is in cm and T is in K. The rate of change of temperature with time is given ($$\alpha = 0.0003 cm^2/sec$$)

A

0.009 K/sec

B

0.0048 K/sec

C

-0.0012 K/sec

D

-0.0018 K/sec