Question 856655
Let's do the sum first.
{{{(1/3)y+(4/9)y=(3/9)y+(4/9)y}}}
{{{(1/3)y+(4/9)y=(7/9)y}}}
Now let {{{y=7}}}
{{{(1/3)y+(4/9)y=(7/9)7}}}
{{{(1/3)y+(4/9)y=49/9}}}