6/9=c/6 what does c equal?

Rai compares two cable plans from different companies. which equation gives the correct value of mm, the number of months for which plans a and b cost the same?

X+ y = 5 ; x - y =3 solve using linear combination

Table which ratio is equivalent to 3: 7? 6: 7 3: 21 24: 56 15: 30