This is the work backward strategy and it is question number 4

Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

Acable company claims that the average household pays $78 a month for a basic cable plan, but it could differ by as much as $20. write an absolute value inequality to determine the range of basic cable plan costs with this cable company. a. |x − 78| ≥ 20 b. |x − 20| ≥ 78 c. |x − 20| ≤ 78 d. |x − 78| ≤ 20

Ineed some on this. not sure how to solve.