Solve the following differential equation with the given boundary conditions.
    - If there are infinitely many solutions, use c for any undetermined constants.
    - If there are no solutions, write No Solution.
    - Write answers as functions of $x$ (i.e. $y=y(x)$).

$$\displaystyle y''+4y = 0$$

• A)     Boundary conditions: $\displaystyle \quad \begin{aligned}[t] y(0) &= 3 \\ y\left(\frac{11\pi }{4}\right) &= -3 \end{aligned}$

      $y =$
  
  

• B)     Boundary conditions: $\displaystyle \quad \begin{aligned}[t] y(0) &= 3 \\ y\left(2\pi \right) &= 3 \end{aligned}$

      $y =$
  
  

• C)     Boundary conditions: $\displaystyle \quad \begin{aligned}[t] y(0) &= 3 \\ y\left(\pi \right) &= -3 \end{aligned}$

      $y =$