Julia buys 4 * 3 = <<4*3=12>>12 pens
Dorothy buys 12/2 = <<12/2=6>>6 pens
The total number of pens purchased is 4 + 12 + 6 = <<4+12+6=22>>22 pens
The total cost of the pens is 22 * $1.50 = $<<22*1.5=33>>33
#### 33