Answer:
12 years younger.
Step-by-step explanation:
Let Jan's age be J and Karyn's age be K.

Jan's age 8 years ago is 2/5 of Karyn's age 4 yeaRs from now.

=> 
=> 4K = 48 X 3
=> K= 36.
=> J= 24.
So Jan is 12 years younger.
The logarithmic expression is

To expand the expression we have to use some properties of logarithm.
We know that 
By using this property we can write,

Square root means to the power 1/2, so for
, we can write
.

Now we have to use another property of logarithm.
We know that, 
So we will use this property to 



Now we have to use another property of logarithm.
We know that, 
By using this property we can write,

This is the required aswer here.