Question 824504
{{{2k + ar = r - 3y}}}
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More than one way, but possible:
Add -r to both, {{{2k+ar+(-r)=r-3y+(-r)}}}
Add -2k to both, {{{2k+ar-r-2r=-3y+(-2k)}}}
{{{ar-r=-3y-2k}}}
Factor r, {{{r(a-1)=-3y+2k}}}
Multiply both by 1/(a-1), {{{highlight(r=(-3y+2k)/(a-1))}}}