Correct Answer: 20

Solution : Here, a + b + c = 5
Squaring both sides, we get,
⇒ (a + b + c) ² = 25
⇒ a ² + b ² + c ² + 2ab + 2bc + 2ca = 25
As, ab + bc + ca = 7
⇒ a ² + b ² + c ² + 2(7) = 25
⇒ a ² + b ² + c ² = 25 – 14 = 11
As we know,
a ³ + b ³ + c ³ = (a + b + c)(a ² + b ² + c ² – ab – bc – ca) + 3abc
As, a + b + c = 5 and ab + bc + ca = 7
⇒ a ³ + b ³ + c ³ = (5)(11 – 7) + 3abc
$\therefore$ a ³ + b ³ + c ³ – 3abc = 20
Hence, the correct answer is 20.