pass two values from checkbox

I want to post of textvalue+checkbox value into the form

<input type="checkbox"id="mycheck2" name="certid[]" value="2" class="cbx"  > 

<input type="number" id="primaryincome2"  min="0"  max="999" name="noc">

I want to get the values like 

1_1
2_1
3_1
4_2

the first value from checkbox and second value from textbox (no of copies)