How much would you need to have made for your spending power to keep with inflation? Your interest rate would have needed to match the inflation rate, otherwise prices are going up faster than you're saving.
How much buying power did you lose? The difference between your required interest and your actual interest. Buying power lost = 1,782 - 1,100 = $682. You lost this much in buying power.
missing angle is 113 degree because the relation between 113 degree and missing angle is that they are alternate interior angle and alternate interior are always equal.