What was the last price of the television set?
Let the cost price = l
Television set was purchased at L-x% of L.
Television set was sold at L-y% of L.
Statement 1=> x=15. This means the television set was purchased at L-15% of L but the value of L (list price) remains unknown. Hence, statement 1 is NOT SUFFICIENT.

Statement 2=> x-y = 5. This establishes a linear relationship between x and y but the value of L (list price) still remains inconclusive. Hence, statement 2 is NOT SUFFICIENT.

Combining both statement together;
x-y=5 where x=15
15-y=5
-y=5-15
-y=-10
y=10.
This provides us with the exact value of x and y but the value of L (wt price) is still unknown. Hence, combining two statements together is NOT SUFFICIENT.

Therefore, option E is the correct answer.