How do you find the initial value on a graph?

Find axis of symmetry and vertex. 8.F.B.4: Construct a function to model a linear relationship between two quantities. Determine the rate of change and initial value of the function from a description of a relationship or from two (x, y) values, including reading these from a table or from a graph.

First subtract 10 from both side
y^2+6y-16=0
(y+8)(y-2)=0
-8 and 2