Reckon, compute (9)
I believe the answer is:
calculate
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">reckon</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >'<span class="explanation-format__original">compute</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for calculate that I've seen before include "'Work out, compute (9)'" , "Compute or reckon" , "Work out mathematically" , "Solve by mathematical procedure" , "Think about" .)