Write the Word or Phrase That Best Completes Each Statement $\$ 75,000$

Write the word or phrase that best completes each statement or answers the question.
-The Jillson's have up to $\$ 75,000$ to invest. They decide that they want to have at least $\$ 40,000$ invested in stable bonds yielding $6 \%$ and that no more than $\$ 20,000$ should be invested in more volatile bonds yielding $12 \%$ .
(a) Using $x$ to denote the amount of money invested in the stable bonds and $y$ the amount invested in the more volatile bonds, write a system of linear inequalities that describe the possible amounts of each investment.
(b) Graph the system of inequalities.