About 18.7 billion tons of agricultural products in our country are exported to foreign countries every year. Among them, about 3.9 billion tons were sold to other Asian countries, about 600 million tons were sold to European countries, and the rest were sold to African countries. How many billion tons of agricultural products does my country sell to African countries every year?
我国的农产品每年约有187亿吨远销国外．其中销往亚洲其他国家的约有39亿吨，销往欧洲国家的约有6亿吨，其余的是销往非洲国家．我国每年向非洲国家销售农产品约为多少亿吨？
<gadget id="calculator">39 + 6</gadget>
<output>45</output>

<gadget id="calculator">187 - 45</gadget>
<output>142</output>

<result>142</result>