The cost of the Smooth Plane after all the discounts can be calculated as follows:
Apply the first discount of 12% to the original price: $195.00 - 12% of $195.00 = $195.00 - $23.40 = $171.60
Apply the second discount of 10% to the new price: $171.60 - 10% of $171.60 = $171.60 - $17.16 = $154.44
Apply the third discount of 3% for paying within 30 days to the new price: $154.44 - 3% of $154.44 = $154.44 - $4.63 = $149.81
So, if the carpenter takes advantage of all the discounts offered, the cost of the Smooth Plane would be approximately $149.81.