basic equation.

Add the given equations, we get :- $2x = 16\\ x = \color{#69047E}{\boxed{8}}$

$Given\quad that\\ \qquad x+y=12\quad ...............\quad (i)\\ \qquad x-y=4\quad ................\quad (ii)\\ Adding\quad (i)\quad \& \quad (ii)\\ we\quad have\\ \qquad 2x=16\\ =>\quad \boxed { x=8 }$

Given:

$X+Y=12$

$X-Y=4$

Substituting, we get:

$X+Y=12$

$X=12-Y$

Putting $X$ in the second equation.

$X-Y=4$

$12-Y-Y=4$

$-2Y=4-12$

$-2Y=-8$

$Y=4$

So, $X=12-Y=12-4=8$

Thus, the answer is: $X=\boxed{8}$

Adding the two equations we get $2x=16$ . Dividing both sides by $2$ , we get $\boxed{x=8}$ .

simple calculation

Adding both the equations, we get 2X = 16.

X = 8.