solve the simultaneous equations 3x+7y=18 and 7x+9y=8

3x+7y=18 (eqn 1)  -multiply by 7->   21x+49y=126 (eqn 1*)

7x+9y=8  (eqn 2)  -multiply by 3->    21x+27y=24 (eqn 2*)

(eqn 1*)-(eqn 2*)  --> 22y=102 therefor y=51/11

sub in this y value back into (eqn1) -->  3x+7(51/11)=18 --> 3x+357/11=18 --> 3x=-159/11

therefore x=-53/11