Solve for: -Variable.mail-

Expression: $1+\left( x+8 \right)=12$

When there is a $+$ in front of an expression in parentheses, the expression remains the same

$1+x+8=12$

Add the numbers

$9+x=12$

Move the constant to the right-hand side and change its sign

$x=12-9$

Subtract the numbers

$x=3$