The cost of 2 pencil, 4 pens and 8 erasers is Rs. 12 and the cost of 8 pens, 10 pencils and 4 erasers is Rs. 36. How much will 3 pencils, 3 pens and 3 erasers cost?

Let say, cost of one pencil,pen and eraser are c, p and e respectively.

So,cost of 2 pencil,4 pens and 8 eraser would be=(2c+4p+8e).

so,(2c+4p+8e)=12..............(1)

Now,cost of 10 pencil,8 pens and 4 eraser would be=(10c+8p+4e).

so,(10c+8p+4e)=36..............(2)

if we add equation (1)&(2) :

$$12c+12p+12e=(12+36).$$

or,$$12c+12p+12e=48$$

or,$$(c+p+e)=4.$$

So,$$3(c+p+e)=3×4=12.$$

So, cost of 3 pencil ,3 pens and 3 erasers would be 12 Rs.

C is correct choice.