Assertion (A) : 2x + y = 8 and 6x + 3y = 20 are two straight lines. To find whether the lines are parallel to each other or not, we need to find the slope of each line.

Reason (R) : If slopes of both the lines are same, they are parallel to each other.

1. A is true, R is false

2. A is false, R is true

3. Both A and R are true and R is the correct reason for A

4. Both A and R are true and R is the incorrect reason for A

We know that,

It is true that if slopes of both the lines are same, they are parallel to each other and in order to find whether two lines are parallel or not we find and compare their slopes.

Hence, Option 2 is the correct option.