12.Cunning manipulations. With the number written on the board, it is allowed to perform the following operations: replace it with its double, or erase its last digit. How can you use these operations to get from the number 458 to the number 14?
12.Let A be the doubling of a number, and B be the erasing of the last digit. Then: $458-\mathrm{B} \Rightarrow 45-\mathrm{A} \Rightarrow 90-\mathrm{B} \Rightarrow 9-\mathrm{A} \Rightarrow 18-\mathrm{A} \Rightarrow 36-\mathrm{A} \Rightarrow 72-\mathrm{B} \Rightarrow 7-\mathrm{A} \Rightarrow 14$.