That means start with some number. Then subtract 3.6 from that number. The result is 0. What number is it that when you subtract 3.6 from it you get 0? That number is 3.6 since 3.6 - 3.6 = 0. That means w, the unknown, must equal 3.6.
That is the explanation.
The way to solve the equation is to see what is being done to the unknown. The unknown here is w. On the left side, you see 3.6 being subtracted from w. In order to undo a subtraction, you must do the opposite operation which is an addition. In order to undo a subtraction of 3.6, you must add 3.6. The rule with equations is that you must do the same operation to both sides of the equation, so add 3.6 to both sides of the equation.
