Use Gaussian elimination or Gauss–Jordan elimination.
Ishikawa Manufacturing borrowed $\$ 30,000$ to buy a new piece of equipment. Part of the money was borrowed at $8 \%$, part at $10 \%$, and part at $12 \% .$ The annual interest was $\$ 3040,$ and the total amount borrowed at $8 \%$ and $10 \%$ was twice the amount borrowed at $12 \% .$ How much was borrowed at each rate?