Breakeven spread analysis advantage, additional, gap, providing

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in vol.4, P.149 Q8, - spread between US and German bonds is 300bps, providing German investors who purchase a US bond with an additional yield income of 75 bps per quarter.  Duration of German bond is 8.3.  If German interest rates should decline, how much of a decline is required to wipe out the yield advantage?
US yield is higher than German yield, shouldn’t German yield (interest rate) increase to close the gap between the two bonds?