Final answer:
To find out the initial length of Jack's porch, subtract the filled length from the total length.
Step-by-step explanation:
To find out how many feet Jack started with on his porch, we can subtract the amount he filled in from the total length of his porch. So, to find the initial length, we can use the equation: Initial Length = Total Length - Filled Length.
Using the given values, we can substitute them into the equation: Initial Length = 42.2 ft - 22.5 ft.
Simplifying the equation, we get: Initial Length = 19.7 ft.