Michael is at driving 50 miles per hour. Which of the following is an equivalent measure of his speed

x = -4 is not undefined because f(x) = x+4 is in the top part, the numerator, not the denominator. So the value that makes f(x) = x + 4 zero does not result in a division by zero.

Indeed, if we try to evaluate (f/g)(-4), then we get

which does not involve a division by zero.

However, attempting to evaluate (f/g)(3) leads us to

which involves a division by zero, and divisions by zero are undefined