A a) x = -3 ; b) (x; y) = (1; -1) , c) x = {0; 3}

B a) x = -3 ; b) (x; y) = (1; -2) , c) x = {0; 3}

C a) x = -3 ; b) (x; y) = (2; -1) , c) x = {0; 3}

D a) x = -3 ; b) (x; y) = (2; 0) , c) x = {0; 3}