Kelsey turned 25 in 1999.  Her older sister was born 3 years before Kelsey.  It's currently 2021.  How old is Kelsey's older sister?
Kelsey turned 25 in 1999 so she was born in 1999-25 = 
<gadget id="calculator">1974</gadget>
<output>1_974</output>
1974.
Kelsey's sister is older by 3 years so she was born in 1974-3 = 
<gadget id="calculator">1974-3</gadget>
<output>1_971</output>
1971.
It's currently 2021 and Kelsey's sister was born in 1971 so she is 2021-1971 = 
<gadget id="calculator">2021-1971</gadget>
<output>50</output>
50 years old.

<result>50</result>