The Achilles tendon connects the muscles in your calf to the back of your foot. When you are sprinting, your Achilles tendon alternately stretches, as you bring your weight down onto your forward foot, and contracts to push you off the ground. A \(70 \mathrm{~kg}\) runner has an Achilles tendon that is \(15 \mathrm{~cm}\) long and has a cross-section area of \(110 \mathrm{~mm}^{2}\), typical values for a person of this size.

a. By how much will the runner's Achilles tendon stretch if the maximum force on it is 8.0 times his weight, a typical value while running?

b. What fraction of the tendon's length does this correspond to?