Answer:
As,it is given that ,Terri is stretching 4 days per week.
It means out of 7 days she is stretching only on 4 days, which can be represented as
.
To increase the frequency variable , Terri must increase her number of days in a week for Stretching.
So, 4<number of days used in stretching ≤7
Which can be represented as either of

So, Option D: 5 days →→Number of days per week Terry need to stretch to increase her frequency variable