Final answer:
The length of line AD is 112 inches.
Step-by-step explanation:
To find the length of line AD, we can use the formula for the area of a triangle: Area = (1/2) * base * height. In this case, line DB is the base and line CD is the height. Given that the area of triangle ABC is 56 square inches, we have:
56 = (1/2) * 10 * 4
Simplifying the equation, we get:
112 = 20
Therefore, the length of line AD is 112 inches.