I guess by slope, you mean gradient.
By knowing the gradient, and a coordinate at which the line passes through, we can use:
y - y1 = m(x - x1)
to get the equation of the line in the form (y = mx + c).
y - 5 = (-3 / 4)(x - 4)
y - 5 = (-3 / 4)x + 3
Rearrange.
y = (-3 / 4)x + 8
Answer:
Corresponding point to (2,8) along -3/4 f(x) = ( -1.5 , -6 )
Explanation:
When a graph f(x) is multiplied by a factor k, the points on the graph also changes by (kx, ky).
Here it is given that (2,8) is on the graph of f(x)
Now we need to find corresponding point to (2,8) along -3/4 f(x)
x - coordinate = 
y - coordinate = 
So corresponding point to (2,8) along -3/4 f(x) = ( -1.5 , -6 )