If 18 inches is 20% less than the original length of the snake, then you can say that it is 80% of the original length. 18 inches ÷ 80% = 0.225, which would be 1% of the original snake. Now that you have 1%, all you need to do is multiply by 100 to get 100%, which is 22.5 inches, which is answer D. I hope this helps!