Sporg  is 8 years old, Sara  is 26 years old.
When Sporg was 7 years old, Sara was 25 years old.
When Sporg was 6 years old, Sara was 24 years old.
When Sporg was 5 years old, Sara was 23 years old.
When Sporg was 4 years old, Sara was 22 years old.
When Sporg was 3 years old, Sara was 21 years old.
When Sporg was 2 years old, Sara was 20 years old.
When Sporg was 1 years old, Sara was 19 years old.
When Sporg was 0 years old, Sara was 18 years old.

Answer: Sara was 18 years old when Sporg was born.

That's the hard way to do it.  Here is the easy way.

Difference in their ages = 26-8 = 18 

So Sara is 18 years older than Sporg.  So when Sporg
was born, he was 0 years old and Sara was 18 years older,
or 18.

Edwin