Let J be Jasmine age and S the sister's age. Then, we have

this equality means Jasmine is 5 years younger than twice her sister's age. Now, we also know that J=39 years then by substituying this value into the last equality, we have

and now, we can solve this equation for S. First, we must move -5 to the right hand side as 5. It reads

and finally, we obtain

therefore, Jasmine's sister has 22 years old.