Nan Nan is going to help her mother make radish and mutton dumplings. The mass ratio of radish to mutton is 3:1. How many grams of mutton are there in 640 grams of stuffing?
楠楠准备帮妈妈包萝卜羊肉饺子，萝卜与羊肉的质量比是3：1，640克的馅中，羊肉有多少克？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">640 * (1/4)</gadget>
<output>160</output>

<result>160</result>