we have
[tex]4.2x-1.4y=2.1[/tex]
Solve for y------> that means isolate the variable y
Subtract [tex]4.2x[/tex] both sides
[tex]4.2x-1.4y-4.2x=2.1-4.2x[/tex]
[tex]-1.4y=2.1-4.2x[/tex]
Divide by [tex]-1.4[/tex] both sides
[tex]y=-\frac{2.1}{1.4} +\frac{4.2}{1.4}x \\ \\y=3x-1.5[/tex]
therefore
the answer is
[tex]y=3x-1.5[/tex]
