The line y = 3x+11 is in slope intercept form y = mx+b where m = 3 is the slope. Anything parallel to this line will also have a slope of 3. Let's plug in m = 3 and (x,y) = (-2,4) which is the point this parallel line goes through.
y = mx+b
y = 3x+b ... replace m with 3
4 = 3(-2)+b ... replace x with -2; replace y with 4
4 = -6+b
4+6 = -6+b+6 ... add 6 to both sides
10 = b
b = 10
Since m = 3 and b = 10, this means that y = mx+b turns into y = 3x+10
