Difference in coefficient estimates

Question

I have simple regression $y_i=\beta_0+\beta_1x+\epsilon$. Then I have estimates $\hat{\beta_0},\hat{\beta_1}$ computed from n observation and estimates $\beta_0',\beta_1'$ computed from n+1 observations. I am asked to derive the difference in those two estimates as a function of sample statistics. I am not even sure how to begin. I started with $\hat{\beta_1}-\beta_1'$ and plugging in $\hat{\beta_1}=\frac{\sum_{i=1}^{n}x_i(y_i-\bar{y})}{\sum_{i=1}^{n}x_i(x_i-\bar{x})}$ and $\beta_1'=\frac{\sum_{i=1}^{n+1}x_i(y_i-\bar{y})}{\sum_{i=1}^{n+1}x_i(x_i-\bar{x})}$ but I couldn't make anything sensible out of this.