Given a function: 

def f(x1, x2):
    a = 5.7e-13
    r = (a * x1) / x2
    return r
	
and 

v1 = 3.97e25 
v2 = 8.45e21  
	
What is the value f(v1, v2)? Please do this step by step I want the entire output in JSON format.
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