Sure.
First, we can find the slope using y2-y1/x2-x1. That gives us:
5-2/8-4, or 3/4.
SInce the slope is m, we already have m. We can plug it into an equation and use the x and y from any of the two coordinates you've given us to find b, or the y intercept. Let's go it.
We'll use (4,2)
2 = 3/4(4) + b
That gives us:
2 = 3 + b
Subtract 3 from both sides to get b = -1.
Therefore, our equation is:
y = 3/4x - 1
Hope this helped!