For

$\begin{matrix} & 1 & 2 & \text{A} \ - & & \text{A} & 9 \ \hline & & 4 & 8 \ \hline \end{matrix}$

the value of digit A is :

1. 6

2. 7

3. -1

4. none of these

$\begin{matrix} & 1 & 2 & \text{A} \ - & & \text{A} & 9 \ \hline & & 4 & 8 \ \hline \end{matrix}$

A - 9 must give a number whose ones digit is 8.

⇒ A - 9 = 8, A - 9 = 18, A - 9 = 28, ……………

⇒ A = 8 + 9, A = 18 + 9, A = 28 + 9, ……………

⇒ A = 17, A = 27, A = 37, ……………

⇒ A = 7, as A is a digit.

Hence, option 2 is the correct option.