The two parts are 3 and 2. Sum of the parts is 5.
So, Sheela gets 3 parts and Sangeetha gets 2 parts out of every 5 parts.
So we can say that
Sheela gets 3/5 of the total pens and Sangeeta gets 2/5 of the total pens.
Number of pens Sheela gets = (3/5) × 20 = 12
Number of pens Sangeeta gets = (2/5) × 20 =8
Therefore, Sheela gets 12 pens and Sangeeta gets 8 pens.