In the following sum, “?”, stands for which digit?
? + 1? + 2? + ?3 + ?1 = 21?	Choices.
A) 4  B) 5  C) 6  D) 7  E) 8
let the digit be x. so the series becomes:   x + (10 + x) + (20 + x) + (10x+3) + (10x + 1)=210 + x   =&gt; 23x + 34 = 210 + x   =&gt; 22x = 176   =&gt;x = 176/22= 
<gadget id="calculator">176/22</gadget>
<output>8</output>
8   ANSW8R:8
<result>E</result>
In the following sum, “?”, stands for which digit?
? + 1? + 2? + ?3 + ?1 = 21?