A 13 - C. If 10a b 7 a b then 10a b 7a 7b and so 3a 6b or more simply a. Add up the digits.
Take away the number you have thought from the answer that is subtract the answer from the number you have thought.
Find the equilibrium price. Think of any three-digit number in which each of the digits is the same. We can form four equations. These math equations went viral for being much more complicated than they seemed - or so simple that.