The number of A is 7930, and the number of B is 20 less than half of it. What is the number of B?
甲数是7930，乙数比它的一半还少20，乙数是多少．
<gadget id="calculator">7_930 / 2</gadget>
<output>3_965</output>

<gadget id="calculator">3_965 - 20</gadget>
<output>3_945</output>

<result>3_945</result>