Question 107496
Let's call M what she needs to invest at 7%. Then,  
{{{20000(0.09)+M(0.07)=5000}}}
{{{1800+0.07M=5000}}}
{{{0.07M=3200}}}
{{{M=3200/0.07}}}
{{{M=45714.29}}}
She'll have to put an additional $45,714.29 at 7% to reach her goal.