For fair value, what is the percentage constitution of customer relationships among the total intangible assets subject to amortization?
{"": {"Fair Value": "(U.S. $ in thousands)", "Useful Life": "(years)"}, "Developed technology": {"Fair Value": 34600, "Useful Life": 5}, "Customer relationships": {"Fair Value": 16900, "Useful Life": 7}, "Backlog": {"Fair Value": 1400, "Useful Life": 3}, "Total intangible assets subject to amortization": {"Fair Value": 52900, "Useful Life": ""}}
fair_value_customer_relationships = df["Customer relationships"]["Fair Value"]
fair_value_total_intangible_assets = df["Total intangible assets subject to amortization"]["Fair Value"]
answer = fair_value_customer_relationships / fair_value_total_intangible_assets * 100.0