A couple has 20,000 dollar to invest for their child's future college expenses. Their accountant recommends placing at least 12,000 dollar in a high-yield mutual fund and at most 6000 dollar in a low-yield mutual fund.
(a) Use $x$ to denote the amount of money placed into the high-yield fund. Use $y$ to denote the amount of money placed into the low-yield fund. Write a system of linear inequalities that describes the possible amounts in each type of account.
(b) Graph the region that represents all possible amounts the couple could place into each account if they wish to follow the accountant's advice.