15) x^2-2x-8=1/4x-1
x^2-2.25x-7=0
4x^2-9x-28=0
(x-4)(4x+7)=0
x-4= 0 or 4x+7=0
x=4 or x= -7/4=-1.75
16) answer hides in the f(x) equation
the trick is to think of the value that will make the (x-4) =0 and and the y value can be directly plugged off from the +c
therefore, ans is x=2 y= 4
(2,4)