c

$\text{The Combination form a real image 3 times larger so m }= -3$

$ \Rightarrow v = -3\times -10cm = 30 cm$

$ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} = \frac{1}{30} - \frac{1}{-10}= \frac{4}{30}$

$ \Rightarrow f = \frac{30}{4} cm$

$\frac{1}{F} = \frac{1}{f_1} +\frac{1}{f_2}$

$ \Rightarrow \frac{1}{f_2} = \frac{4}{30} - \frac{1}{-30} = \frac{5}{30}$

$\Rightarrow f_2 = 6cm$

$\text{Its a convex lens of focal length 6cm}$