Can I erect a 9-inch wall over a 4-inch reinforced concrete slab?

I think you can design slab for taking load of 9" brick wall. First check that slab can take one way acting shear generated due to load. considering 9" wall weigh 0.54 t/sqm /m height and 3.0 m height of wall will have load of 0.54*3=1.62 t/m length. As load is transferred through two edges ,each edge will have shear force of 0.81 t/m. hence depending upon thickness of slab and % of steel the shear stress will be t_v if this is less than t_c then load transfer is o.k. Considering the line load on the slab identify effective width for calculation of B.M. per unit length and then design the slab.

However as in any other case since slab is supporting wall, as rightly pointed deflection will have to be checked so that additional deflection is not greater than span/350 or 20 mm whichever is lower.