We know that if two lines are Parallel then both the lines have same Slope.
Given : Equation of 1st Parallel line is 3x + y = 6
this can be written as :
y = -3x + 6
Comparing with standard form : y = mx + c
we can notice that slope = -3
We know that the form of line passing through point (x₀ , y₀) and having slope m is :
y - y₀ = m(x - x₀)
Here the 2nd Parallel line passes through the point (-2 , 8)
x₀ = -2 and y₀ = 8 and we found m = -3
⇒ y - 8 = -3(x + 2)
⇒ y - 8 = -3x - 6
⇒ -3x - y = -2
⇒ 3x + y = 2