if you graph y=-x^2-8x+10, what would your y-intercept be?

@@    Alan's graph is good but you need to read what I have written!

The equation of the y axis is x=0   (No matter what the y value is, the x will always be equal to 0)

So if you want to know what the y intercept is, you just substitute in x=0

y=0-0+10

the y intercept is 10

For questions of this form, the y intercept is the constant on the end.  But it is much better if you understand why. 

Perhaps this graph will help.