Chelsea took out three loans for a total of $120,000. Her Bank Loan was at an interest rate of 8%, the small business loan was at an interest rate of 5%, the mortgage on her house was at an interest rate of 4%. The total simple interest due on the loans in one year was $5750. The annual simple interest on the mortage was $1600 more than the interest on the bank loan. How much did she borrow from each source?
"I can only get this far"
x+y+z=120,000 first equation
.8x + .5y + .4z=5750 second equation
z=1600 + x third equation
the answers are x=$15,000 y=$35,000 z=$70,000
how did they work this out????