The cost of 21 pencils and 9 pens is ₹276, and the cost of 6 pencils and 3 pens is ₹84. The cost of 1 pencil and 1 pen is:

Let the cost of 1 pencil be x and the cost of 1 pen be y.
From the given statements, we form two linear equations:

21x+9y=276

6x+3y=84

Let's simplify Equation (2) by dividing the whole equation by 3:

2x+y=28⟹y=28−2x
Substitute y into Equation (1):

21x+9(28−2x)=276
21x+252−18x=276
3x=276−252
3x=24⟹x=8
Now find y:

y=28−2(8)=28−16=12
Thus, the cost of 1 pencil and 1 pen combined is:

x+y=8+12=₹20