Answer: {x,y} = {27/4,-47/8}
You need to simplify it first.

Use distribution

y=mx+b
m=slope
your slope is -4 :)
It has a minimum value at x = 3 and f(x) = 4
Vertex form is
f(x) = a(x - 3)^2 + 4 where a is some constant to be found
From the graph when x = 5 f(x) = 15, so
15 = a * 2^2 + 4
a = 15-4/4 = 11/4
so our equation is f(x) = 11/4(x - 3)^2 + 4