we simplify the equation to the form, which is simple to understand
13+w/7=-18
simplifying
13+0.142857142857w=-18
we move all terms containing w to the left and all the other terms to the right
+ 0.142857142857w=-18-13
we simplify left and right side of the equation
+ 0.142857142857w=-31
we divide both sides of the equation by 0.142857142857 to get w
w=-217
