If p is price per bushel and xx is supply (in million bushels), then it must be true that

\(\displaystyle{3.20}={9800}{m}+{b}\)

\(\displaystyle{2.95}={9300}{m}+{b}\)

Subtracting these two equations, we get

\(\displaystyle{0.25}={500}{m}\)

Divide both sides by 500 to get \(\displaystyle{m}={0.00055}.\)

Now substitute this into the first equation to get

\(\displaystyle{3.20}={9800}⋅{0.0005}+{b}\)

\(\displaystyle{3.20}={4.9}+{b}\)

Subtract 4.9 on both sides to get \(\displaystyle{b}=−{1.7}\)

Now that we know both parameters, we can write down the general form

\(\displaystyle{p}={0.0005}{x}−{1.7}\)

\(\displaystyle{3.20}={9800}{m}+{b}\)

\(\displaystyle{2.95}={9300}{m}+{b}\)

Subtracting these two equations, we get

\(\displaystyle{0.25}={500}{m}\)

Divide both sides by 500 to get \(\displaystyle{m}={0.00055}.\)

Now substitute this into the first equation to get

\(\displaystyle{3.20}={9800}⋅{0.0005}+{b}\)

\(\displaystyle{3.20}={4.9}+{b}\)

Subtract 4.9 on both sides to get \(\displaystyle{b}=−{1.7}\)

Now that we know both parameters, we can write down the general form

\(\displaystyle{p}={0.0005}{x}−{1.7}\)