Estimator for $B_1$ in $B_0+B_1x$

Question

According to my book, the Estimator for $B_1$ is given by

$B_1 =\dfrac{\sum_{i=1}^n(x_i-\bar x)(Y_i\color{red}{-\bar Y})}{\sum_{i=1}^n(x_i-\bar x)^2} = \dfrac{\sum_{i=1}^n(x_i-\bar x)Y_i}{\sum_{i=1}^n(x_i-\bar x)^2}$

Why is it obvious that $-\bar Y$ can be omitted?

Answer 1

$$\sum_{i=1}^n\bar{Y}(x_i-\bar{x})=\bar{Y}\sum_{i=1}^n(x_i-\bar{x})=0$$

since $\sum_{i=1}^n(x_i-\bar{x})=0$