Subtract 2.1 from both sides:
[tex]4.2x-1.4y-2.1=0 [/tex]
Add 1.4y to both sides:
[tex] 4.2x-2.1=1.4y[/tex]
Of course, we can rewrite this as
[tex] 1.4y=4.2x-2.1[/tex]
Divide both sides by 1.4
[tex] y = \dfrac{4.2}{1.4}x - \dfrac{2.1}{1.4} = 3x - 1.5 [/tex]
