Final answer:
If the interest rate is 9%, Gizmo will invest in projects that yield a return of 14% or higher if it considers the social benefits.
Step-by-step explanation:
The Gizmo Company's investment in R&D would depend on the going interest rate and the private and social benefits of the investment. If the interest rate is 9% and the company only considers the private benefits, it would invest in projects that yield a return equal to or higher than the interest rate. However, if the company also considers the social benefits, which are 5% higher than the private benefits, it would invest in projects that yield a return of 9% + 5% = 14% or higher.