If 2 mole of an ideal monoatomic gas at temperature $$T$$, is mixed with 6 mole of another ideal monoatomic gas at temperature $$2T$$ then the temperature of mixture is :

A

$$\dfrac{5}{2}T$$

B

$$\dfrac{5}{4}T$$

C

$$\dfrac{7}{2}T$$

D

$$\dfrac{7}{4}T$$