Last month, corporations supplied $250 billion in one-year discount bonds to investors at an average market rate

Question:

Last month, corporations supplied $250 billion in one-year discount bonds to investors at an average market rate of 11.8%. This month, an additional $25 billion in one-year discount bonds became available, and market rates increased to 12.2%. Assuming that the demand curve remained constant, derive a linear equation for the demand for bonds, using prices instead of interest rates.