First, add #color(red)(2s)# and subtract #color(blue)(14)# from each side of the equation to isolate the #s# term in a positive form while keeping the equation balanced:
#r - 2s + color(red)(2s) - color(blue)(14) = 14 + color(red)(2s) - color(blue)(14)#
#r - color(blue)(14) - 2s + color(red)(2s) = 14 - color(blue)(14) + color(red)(2s)#
#r - color(blue)(14) - 0 = 0 + color(red)(2s)#
#r - 14 = 2s#
Now, divide each side of the equation by #color(red)(2)# to solve for #s# while keeping the equation balanced:
#(r - 14)/color(red)(2) = (2s)/color(red)(2)#
#(r - 14)/2 = (color(red)(cancel(color(black)(2)))s)/cancel(color(red)(2))#
#(r - 14)/2 = s#
#s = (r - 14)/2#
Or
#s = r/2 - 14/2#
#s = r/2 - 7#