We simplify the equation to the form, which is simple to understand
r+31=-2(6r+4)
Reorder the terms in parentheses
r+31=+(-12r-8)
Remove unnecessary parentheses
+r+31=-12r-8
We move all terms containing r to the left and all other terms to the right.
+1r+12r=-8-31
We simplify left and right side of the equation.
+13r=-39
We divide both sides of the equation by 13 to get r.
r=-3