Are you reading Arithmetica by Diophantus (3rd century AD)? Mathematicians started using +, - and * to write equations in the 16th century...

The phrase "that number subtracted from 2 times 6" is ambiguous. It may mean "(that number subtracted from 2) times 6" or "that number subtracted from (2 times 6)." In fact, the latter possibility is less likely because problem statements usually don't contain parts that can be easily simplified. (E.g., I would be surprised to see a problem saying, "A car goes from A to be at (30 + 40) miles per hour" instead of "at 70 miles per hour.")

Suppose the problem says "Three times a number is the same as (that number subtracted from 2) times 6." Denote the number by x. Then x subtracted from 2 is 2 - x. Therefore, the equation is 3x = 6(2 - x). However, its solution is not in the list.

Suppose the problem says "Three times a number is the same as that number subtracted from (2 times 6)." Then the equation is 3x = 2 * 6 - x, which gives the answer (D).

You apparently thought that "that number subtracted from 2 times 6" means x - 12. Then the equation is 3x = x - 12, i.e., x = -6. But this interpretation is incorrect.