The slab works like a one way continuous slab, supported by walls which in this case are beams. It could proceed  to use the methods for continuous beams (slabs in this case) adopting linear-elastic methods (moment distribution, stiffness methods, etc.) or using moment re-distribution. But, in most cases a simplified “coefficient”method is easier. The method applies when:
ratio of adjacent span lengths <= 1.2
loads are essentially UDL -g and q
q <= 2 g
slab is of uniform section
rebar layout complies with Code arrangement
actions at supports are solely due to slab loads

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