Simplify 2a² -4ab - 6a² - 10ab + 5ab - 5a²

A boy leaves station X on a bearing of 035° to station y which is 21km away. He then travels to another station Z on a bearing of 125°. If Z is directly East of X, what is the distance from X to his present position?

The length, breadth and height of a cuboid are 8cm, 7\(\frac{1}{2}\)cm and 6\(\frac{1}{2}\) cm respectively. What Is its volume in m³ (leave your answer in standard form)?

Find the surface area of a sphere whose radius is 3.5cm, correct your answer to one decimal place (π = \(\frac{22}{5}\))