We know that,

a³ + b³ = (a + b) (a² – a × b + b²)

Using this formula, we get

= (a)³ + (0.2)³

= (a + 0.2) [(a)² – a (0.2) + (0.2)²]

= (a + 0.2) (a² – 0.2a + 0.04)