Question 136579
Let x be one number.

Given {{{y = x + 12}}} and {{{x + 2y = 39}}}

Use substitution to solve for y as follows:

{{{y = x + 12}}} --> {{{y-12=x}}}
{{{x + 2y = 39}}}
{{{(y-12) + 2y = 39}}}
{{{3y-12 = 39 }}}
{{{3y = 51}}}
{{{y = 17}}}

Check your answer. {{{x = y-12}}} = 5. Does {{{5 + 2*17 = 39}}} ??