The question asks to calculate the variance for $\hat{\beta}$. I've checked the solutions and I don't know why the denominator is squared. What formula is that?
$$ Var\left(\hat\beta\right) = Var\left(\frac{\sum_{i=1}^n(x_i-\bar{x})Y_i}{\sum_{i=1}^{n}(x_i-\bar{x})^{2}}\right) = \frac{Var\left(\sum_{i=1}^n(x_i-\bar{x})Y_i\right)}{\left(\sum_{i=1}^n(x_i-\bar x)^2\right)^{2}} $$
The full question, with the initial information about the data:
