Parallel means it has the same slope -1/3
The -4 is where there line crosses the y axis. The general form of a line is y = mx + b where m is the slope and b is where is crosses the y axis.
All you have so far is the slope = -1/3 so y = -1/3 x + b
But it must also go through ( -6, -3 ) where x = -6 and y = -3
Now substitute those values into y = -1/3 x = b and you get -3 = -1/3 (-6) + b
Or -3 = 2 + b
I will let you finish it to get the value of "b" and the line that is parallel and goes through ( -6, -3 )
I hope this helps.
Harvey M