Uncle Zhang surrounded a rectangular vegetable field by the wall at the back of the house. It is 10 meters long and 70 meters wide. He has a fence to surround the three sides that are not against the wall. How many meters of fence should be used at least?
张大爷在房后靠墙圈了一块长方形菜地，长10米，宽70米，他有篱笆把不靠墙的三边围了起来，至少得用多少米篱笆？
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">70 + 20</gadget>
<output>90</output>

<result>90</result>