Zeta Automotive Limited (ZAL) has designed a new engine component (code name FE73) that can potentially increase

Question:

Zeta Automotive Limited (ZAL) has designed a new engine component (code name FE73) that can potentially increase the fuel efficiency of a car to approximately 72 miles per gallon. ZAL supplies its components to automotive assembly plants. The automotive assembly plants want assurance that each FE73 can provide fuel efficiency of between 70 and 75 miles per gallon at the Six Sigma quality level.
What should be the standard deviation for FE73 to achieve Six Sigma quality?