Given equation is 
To find the x coordinate of vertex we use formula

From the given equation a= 2, b= 8 and c= -5
Plug in all the values

The x coordinate of vertex is x=-2
To find y coordinate of vertex we plug in -2 for x in the given equation


So vertex is (-2,-13)
It's very easy, just try raising 5 to different powers until you get 125.
5^1 = 5
5^2 = 5*5 = 25
5^3 = 25*5 = 125
Ah, x is 3!