To solve this problem, we can use the formula for joint variation, which states that A varies jointly as R1 and R2 if A = k*R1*R2, where k is a constant of variation.
Additionally, we know that A varies inversely as the square of L, which means that A = k*R1*R2/L^2.
Plugging in the given values, we get:
A = k*R1*R2/L^2
A = 2*120*8/5^2
A = 3.84
Therefore, when R1=120, R2=8, L=5, and k=2, A is equal to 3.84.