Proper way to solve function notations? I'm just starting to use function notation and I'm wondering if I'm solving correctly.
If $f(x) = 4x - 11$, determine 
a. $f (1/4)$
$f(x) = 4x - 11$
$f(1/4) = 4 (1/4) - 11$
$f(1/4) = 1 - 11 $
$f(1/4) = -10$
b. $f(-3)=4x-11$
$f(-3)=4(-3)-11$
$f(-3)= -12-11$
$f(-3) = -23$
The equation $C=10n+45$ represents the total cost, C dollars, for a sports banquet , when n people attend. 
a. Describe the function in words and then express the function using function notation.
b. Determine C(250) and explain what the result represents.
c(250)=10n+45
c(250)=10(250)+45
c(250)=2545
c. If the total cost of the banquet is C(n) = 4295, find n, the number of people attending the banquet.
4295 = 10n + 45
45+4295=10n+45+45
4340 / 10 90 / 10
434-9= 425
425 x 10 + 45 = 4295
425

All your answers are correct.
However the redaction for the solution of $C(n)=4295$ is not very clear, particularly the line "4340 / 10 90 / 10". Here is how I would do it
$$\begin{array}{l|r}C(n)=4295 & \\ \iff 4295=10n+45 &\quad -45\\ \iff 4250 = 10n & \div 10\\ \iff 425 = n\end{array}$$
