In a certain language, the numbers are coded as follows : How is the number…

In a number-letter substitution code, each digit given in the key stands for one fixed letter; to code any new number, its digits are read left to right and each digit is replaced by its assigned letter in the same order, giving one letter per digit.

1. From the key: 4 → A, 3 → W, 9 → P, 2 → Q, 1 → R, 6 → B.

2. The number to be coded is 439216, whose digits in order are 4, 3, 9, 2, 1, 6.

3. Substituting each digit's letter in the same order: 4→A, 3→W, 9→P, 2→Q, 1→R, 6→B.

4. Combining these letters in order gives the code AWPQRB.

A one-to-one digit-to-letter substitution of a 6-digit number must yield exactly 6 letters — AWPQRB has six letters, matching the six digits of 439216, confirming the substitution is complete and correctly ordered. (The key image lists the digit 2 twice — once against Q and once against J. Only Q is used here: J appears in none of the four given options, while using Q for digit 2 produces the valid six-letter code AWPQRB that matches one of them.)