Answer:
- 10
Step-by-step explanation:
Substitute k = 3, 4, 5, 6 into the expression and sum the terms, that is
(- 15 + 20) + (- 20 + 20) + (- 25 + 20) + (- 30 + 20)
= 5 + 0 - 5 - 10
= - 10
