Hassan predicted that he would sell 178 postcards. He actually sold 142 postcards. What are the values of a and b in the table below? Percent Error Item Approximate value Exact value Error Absolute error Ratio Percent error Postcards 178 142 a b a = negative 36; b = negative 36 a = negative 36; b = 36 a = 36; b = negative 36 a = 36; b = 36