Question 816750
simple interest is calculated with this formula I = prt, where p is principal, r is rate and t is time,
in this case t is 1 year
0.04x +0.045(12000-x)=525  is setup correctly
0.04x +540 -0.045x = 525
-0.005x = -15
x = 3000
The problem asks us how much money was invested at 4% and 4.5% given that Phyllis had $12,000 to invest.  Our calculation shows the following
$3,000 invested at 4%
$9,000 invested at 4.5%
We are also told that Phyllis earned $525 in interest from both investments
now check the answers
0.04*3000 + 0.045*9000 = $120 + $405 = $525
our answers check