#### Answer

Not a solution

#### Work Step by Step

We can determine whether or not the given number is a solution of the given equation by plugging in the number into the equation.
If both sides of the equation are equal after plugging in the number, we know that the given number is a solution.
$4=1-x$
$1-(5)=1-5=1+(-5)=-4\ne4$
Therefore, $x=5$ is not a solution.