since you're not given any other data then i presume that you are asked x in terms of y. then you'll have
[tex]y = \frac{4x}{7y} + 6
[/tex]
[tex]y = \frac{4x +7y(6)}{7y} [/tex]
[tex]7y(y) = 4x + 42y[/tex]
[tex]7y^2 = 4x +42y[/tex]
[tex]7y^2 - 42y = 4x[/tex]
[tex]x = \frac{7y^2 - 42y}{4} [/tex]
