The following rational equation has denominators that contain variables. For this equation, a$.$ Write the value or values of the variable that make a denominator zero. These are the restrictions on the variable. $b.$ Keeping the restrictions in mind, solve the equation.

$\frac{3}{x+3}+\frac{5}{x-4}=\frac{35}{(x+3)(x-4)}$

a$.$ What is$/$are the value or values of the variable that make$($s$)$ the denominators zero?

$x=$

$($Simplify your answer. Use a comma to separate answers as needed.$)$