Question 698569
One problem at a time please.
(1)solve for y in 3x+7y = 6x+1
3x+7y = 6x+1 subtract 3x from each side of the equal sign
7y=3x+1 divide each side by 7
{{{y=(3x+1)/7}}}

(2)solve the system of equation:  
2x+5y =2
-7x+4y =20
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2x+5y =2  multiply this equation by  7
-7x+4y =20 multiply this equation by 2

14x+35y=14
-14x+8y=40   now add the two equations
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43y=54   divide both sides by 43
{{{y=54/43}}} now plug that into either of the original equations, i'll use first one, and solve for x
{{{2x+5(54/43)=2}}}
{{{2x+270/43=2}}} subtract 270/43 from each side
{{{2x=86/43-270/43}}}
{{{2x=(86-270)/43}}}
{{{2x=(-184)/43}}} divide each side by 2
{{{x=(-184)/86=-92/43}}}