4 pens x Qr 4 = 16
16 rubbers x Qr 0.25 = 4

or

3 pens x Qr 4 = 12
15 pencils x Qr 0.5 = 7.5
2 rubbers x Qr 0.25 = 0.5

Both Total 20 items and Qr 20