y = mx + b
m is the slope
b is the y-intercept.
if your know the slope, then just replace m with it and solve for b by replacing x and y in the equation with the value of one of the points.
in your problem, m = 3/4 and the point that it goes through is (x,y) = (5,-4)
replace m with 3/4 and replace x with 5 and y with -4 to get:
y = mx + b becomes -4 = 3/4 * 5 + b
simplify to get:
-4 = 3.75 + b
subtract 3.75 from both sides of the equation to get:
-4 - 3.75 = b
solve for b to get:
b = -7.75
the equation becomes:
y = 3/4 * x - 7.7 5
the graph of the equation looks like this.
you can see that the y-intercept (the value of y when x = 0) is -7.75 and that the graph of the equation goes through the point (x,y) = (5,-4).