Why can't the number eleven called like onetey one?

Answer 1

just speculating ... we have 20 digits (fingers and toes)

so those numbers have unique names

starting with 20 , the numbers one through nine are just "tacked on"
... twenty-one , twenty-two , etc

same with thirty , forty , fifty , etc

Answer 2

5x + 2y = -4
-5x + 3y = 19