Question 665659
Starting with
{{{3/7}}}(21y+14) - 3(4y+7) = 0
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Distribute the {{{3/7}}} and the 3
{{{3/7}}}(21y)+ {{{3/7}}}(14) - 3(4y) -3(7) = 0
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Multiply
{{{3/1cross(7)}}}{{{3cross(21)y}}} + {{{3/1cross(7)}}}{{{2cross(14)}}} - 12y - 21 = 0
9y + 6 - 12y - 21 = 0
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Combine like terms
{{{highlight(9y)}}} + 6 - {{{highlight(12y)}}} - 21 = 0
-3y + {{{highlight(6)}}} - {{{highlight(21)}}} = 0
-3y - 15 = 0
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Isolate y
-3y - {{{cross(15)}}} + {{{cross(15)}}} = 0 + 15
-3y = 15
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Divide both sides by -3
{{{cross(-3)y/cross(-3) = 15/-3}}}
y = -5
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Check {{{cartoon(
(3/7)(21(-5) + 14) - 3(4(-5) + 7) = 0,
(3/7)(highlight(-105) + 14) - 3(highlight(-20) + 7) = 0,
(3/7)(highlight(-91)) - 3(highlight(-13)) = 0,
-39 + 39 = 0)}}}