In four years, Peter will be twice as old as Harriet. If Peter's age is currently half of his mother's age, who is 60, how old is Harriet now?
If Peter's age is currently half of his mother's age, who is 60, Peter is 1/2*60 = 
<gadget id="calculator">30</gadget>
<output>30</output>
30 years old.
In four years, Peter will be 30+4 = 
<gadget id="calculator">30+4</gadget>
<output>34</output>
34 years old.
Since Peter's age in four years will be twice Harriet's age, Harriet will be 34/2 = 
<gadget id="calculator">34/2</gadget>
<output>17</output>
17 years old in four years.
Currently, Harriet is 17-4 = 
<gadget id="calculator">17-4</gadget>
<output>13</output>
13 years old.

<result>13</result>