Answer
Phyllis invested \$9000 at 4.5% and the rest (\$3000) at 4%.
Work Step by Step
Let $x$ be the amount invested at 4.5% and $12000-x$ be the amount invested at 4%. Thus the total earnings would be:
Total earnings = $0.045*x+(12000-x)*0.04 = 525$
We solve for $x$:
$0.045*x+480-0.04x=525$
$0.005*x+480=525$
$0.005*x=45$
$x=9000$
Thus Phyllis invested \$9000 at 4.5% and the rest (\$12000-\$9000=\$3000) at 4%.
