how to solve (1.06)^4 quickly?

1+nx+(x^2)*(n(n-1)/2) approximation.

how we can increase speed

Hai Gunjan, In any exam, speed and accuracy play an important role. Speed can be achieved only through extensive practice. In verbal or English language Speed can be achieved through extensive reading habits, practice. In Reasoning, Quantitative Aptitude, Speed can be achieved through Conceptual clarity & practicing of Vedic Maths for speedy calculations. Squares, Cubes & formulae should be on your finger tips.