a) To apply the first discount we need to calculate 12% of the price ($350).

Considering this discount only, the cost of the product now is $350 - $42 = $308
Now, we need to apply the second discount to this new price. 8% of $308 is computed as follows:

Then, the total discount is:

b) To calculate the total discount as a percent, we need to find what percent (x) represents $66.64 with respect to $350 (which represents 100%). We can do this with the help of the next proportion:

Solving for x:

As a percent, the total discount is 19.04%