Uncle Wang bought a house worth 800,000 yuan, with a down payment of 40%, and the rest of the loan for 20 years, with an annual interest rate of 7.8%. How much interest does Uncle Wang have to pay in total?
王叔叔买了一套价值80万元的房子，首付40%，其余的贷款20年，年利率7.8%．王叔叔一共要支付多少利息？
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">80 * (2/5)</gadget>
<output>32</output>

<gadget id="calculator">80 - 32</gadget>
<output>48</output>

<gadget id="calculator">7.8 / 100</gadget>
<output>0.078</output>

<gadget id="calculator">48 * 20 * 0.078</gadget>
<output>74.88</output>

<result>74.88</result>