If [math]4a = e[/math], [math]\frac{b}{4} = e[/math], [math]c + 4 = e[/math], [math]d - 4 = e[/math] and [math]a + b + c + d = 100[/math], then what is the value of [math]e[/math]? What is the best linear equation used in math?