Question 188514
You are trying to find 'c' -- the distance between the vertex and the focus.
Think of the equation for a vertical parabola:
y = (1/4c)(x-h)^2 + k
If we place our parabola at the center our equation becomes:
y = (1/4c)x^2
.
The problem gives you a point on the parabola: (10,4)
Plug it in and solve for 'c':
y = (1/4c)x^2
4 = (1/4c)10^2
4 = (1/4c)100
4 = (1/c)25
4c = 25
c = 25/4
c = 6.25 feet