Jean is two years older than Mark.  Two years ago Mark was 5 years older than half Jan's age.  If Jan is 30 how old is Jean?
2 years ago Jan was 30-2=
<gadget id="calculator">30-2</gadget>
<output>28</output>
28 years old.
So Marks age two years ago was 5+28/2=
<gadget id="calculator">5+28/2</gadget>
<output>19</output>
19 years old.
Mark is now 19+2=
<gadget id="calculator">19+2</gadget>
<output>21</output>
21 years old.
So Jean is 21+2=
<gadget id="calculator">21+2</gadget>
<output>23</output>
23 years old.

<result>23</result>