Answer:
Let's kim's sisters age be 2x and kim's age be x.
★ When we add kim's age to her sister age, they equals to 36.
So, the equation becomes -
[tex] \\ \implies \sf \: x + 2x = 36 \\ \\ \\ \implies \sf \: 3x = 36 \\ \\ \\ \sf \underline{Now, \: \: solve \: \: for \: x \: \: - } \\ \\ \\ \implies\sf \: x = \frac{36}{3} \\ \\ \\ \implies \large{ \boxed{ \sf{ x = 12}}} \\ [/tex]