We shall have to use distribution here.
The number outside the parenthesis gets distribute with the numbers inside.
This is called distributive property.
We know the distributive property is
a(b+c) = a × b + a ×c
Using this property for
5(4 x+2)
= 5× 4x + 5 × 2
Now 5 times 4x = 20x
5 times 2 = 10
So we get
5(4 x+2) = 20 x + 10
Option A) is the right answer.