N+4=13
-4 -4
n = 9
the sum of a number(n) and 4 that is no larger than 13 is 9
See the attached picture:
State the vertex and axis of symmetry of the graph of y=ax^2+c
General form of quadratic equation is 
There is no bx in our given equation, so we put 0x
Given equation can be written as 
a=a , b=0
Now we use formula to find vertex


Now we plug in 0 for 'a' and find out y

So our vertex is (0,c)
The axis of symmetry at x coordinate of vertex
So x=0 is our axis of symmetry
Basically you canceling out and your answer is R= 1/2