Which of the following equations best describes the linear relationship shown in the table, where $g$ represents the number of pounds of grain sold and $d$ represents the price in dollars of one pound of grain?
a.$g = 1.2 d+12,500$
b.$g = 12,500 d+15,000$
c.$g$ = $-12,500 d+17,500$
d.$g$ =$-12,500 d+30,000$