Final answer:
The value of R when a is 5 can be found using the inverse proportionality relationship R = k/a, yielding R = 3.6.
Step-by-step explanation:
The question involves understanding and working with an inverse proportion. To solve this, you need to set up an equation based on the fact that R is inversely proportional to a. We can write this as R = k/a, where k is the constant of proportionality. Using the given values, when R is 12 and a is 1.5, you can find k by multiplying 12 by 1.5, giving you k = 18. Now to find the value of R when a is 5, you would use the same constant, k = 18, and divide it by the new value of a, which is 5. Therefore, R = 18 / 5, which simplifies to R = 3.6.