how can i make 1 1/2 cup of all purpose flour to 1 1/2 cup of self'rising flour?
This article has a pretty typical ratio:

1 c. flour : 1 1/2 tsp baking powder : 1/4 tsp salt

so for 1 1/2 cup, you would want:

1.2 c. flour, 2 1/4 tsp baking powder : 3/8 tsp salt

Alternatively, you could make a fairly large batch, whisk it together well, then measure normally.