Answer:
C.

General Formulas and Concepts:
Calculus
- Mean Value Theorem (MVT) - If f is continuous on interval [a, b], then there is a c∈[a, b] such that

- MVT is also Average Value
Explanation:
Step 1: Define

f'(c) = 20
Interval [1, b]
Step 2: Check/Identify
Function [1, b] is continuous.
Derivative [1, b] is continuous.
∴ There exists a c∈[1, b] such that

Step 3: Mean Value Theorem
- Substitute:

- Rewrite:

And we have our final answer!