Slope intercept form is:
y = mx + b
"m" is the slope, "b" is the y-intercept (when x = 0)
I'm assuming that the equation of a line is parallel to the given line.
When lines are parallel, they have the same slope.
The given line's slope is 4, so the parallel line's slope is also 4
y = mx + b
y = 4x + b
To find b, you plug in the point (4,8) into the equation.
y = 4x + b
8 = 4(4) + b
8 = 16 + b Subtract 16 on both sides
-8 = b
Your equation is:
y = 4x - 8