He needs 12 tablespoons of lemon juice for every dozen of cupcakes and he’s making 3 dozen cupcakes so he needs 12*3 = <<12*3=36>>36 tablespoons of lemon juice
1 lemon provides 4 tablespoons of lemon juice and he needs 36 tablespoons so he will need 36/4 = <<36/4=9>>9 lemons
#### 9