What asian dragon moved to the core?

Geologists know that potassium-40 decays to argon-40, with a half-life of 1.3 billion years. if an analysis of a feldspar crystal in a sample of granite shows that 75 percent of the potassium-40 atoms have decayed to form argon-40, what is the age of the granite

In the diagram below dab and dac are adjacent angles

Suggest 3 different reasons why there is an ageing population in the uk .