Question: genmatrix when unkowns are functions

I have a system of equations where unkowns are functions of variables > eqns:= {a(s,y,z,t)+2*b(s,y,z,t)=0,3*a(s,y,z,t)-5*b(s,y,z,t)=0}; I would like to get the matrix associated to the system. I tested genmatrix but maple returns `equations are not linear ` Anyone have an idea of how to do this?
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