Mr. Zhang bought 1,000 yuan of 5-year treasury bonds issued by the Industrial and Commercial Bank of China on July 8, 1998. After returning home, he recorded on the back of the deposit receipt that he could get the treasury bonds when they expired on July 8, 2003. The amount of interest is 390 yuan. If Mr. Zhang's calculation is correct, what is the annual interest rate of this type of treasury bill?
张先生于1998年7月8日买入中国工商银行发行的5年期国库券1000元，回家后他在存单的背面记下了当国库券于2003年7月8日到期后他可获得的利息数为390元，若张先生计算无误的话，则该种国库券的年利率是多少？
<gadget id="calculator">5 * 1_000</gadget>
<output>5_000</output>

<gadget id="calculator">390 / 5_000</gadget>
<output>39/500 = around 0.078</output>

<result>39/500 = around 0.078</result>