First degree equation;:
A term that changes member changes sign
Fractions: Multiply the 2 members by the nominators least common multiple
Go !
$1 + x = 3$
$x = 3-1\qquad : \qquad S=\{2\}$
$3+x=-x+3$
$x+x = 3-3 \qquad;\qquad 2x = 0\qquad ;\qquad S =\{0\} $
$3+x=x+3$
$x-x = 3-3 \qquad;\qquad 0x = 0\qquad ;\qquad S = \mathbb R $ ( All real numbers are solution !)