Question: "How can I solve this error in Maple?"

5*x-7 = 3*x+2;
                             "(->)"
lhs(5*x-7 = 3*x+2) - rhs(5*x-7 = 3*x+2) = 0;
                          2 x - 9 = 0
                              [x]
isolate( 2*x-9 = 0, %ARG1 );
Error, (in isolate) 2*x-9 = 0 does not contain %ARG1
plz explain me what is this error?

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