A table is given the data: table
Based on this table, we computed
$\sum_{i=1}^{n} X_{i1}^2 = 471$, $\sum_{i=1}^{n} X_{i2}^2 = 163.84$, $\sum_{i=1}^{n} X_{i1}X_{i2} = 235$
$\sum_{i=1}^{n} X_{i1}Y_i = 4915.3$, $\sum_{i=1}^{n} X_{i2}Y_i = 3103.66$
We consider the following model involving both independent variables and an intercept: $$Y_i = \beta_0 + \beta_1X_{i1} + \beta_2X_{i2} + \epsilon_i$$
where $\beta_j, j = 0,1,2$ are $3$ parameters and $\epsilon_i$ are pairwise indepedent random errors with mean $0$ and common variance $\sigma^2$. In the matrix notation, the model is
$$Y = X \beta + \epsilon$$
$$ X= \begin{bmatrix} 1 & 7 & 2.6\\ 1 & 1 & 2.9\\ 1 & 11 & 5.6\\ 1 & 11 & 3.1\\ 1 & 7 & 5.2\\ 1 & 11 & 5.5\\ 1 & 3 & 7.1 \end{bmatrix} $$
$$ Y= \begin{bmatrix} 78.5 \\ 74.3 \\ 104.3 \\ 87.6 \\ 95.9 \\ 109.2 \\ 102.7 \end{bmatrix} $$
(a) how do I calculate XX?
Hint: It´s almost sure that it is a typo. The formula for the estimated parameters $\beta_0, \beta_1$ and $\beta_2$ is
$$ \hat{ \beta} =\left(\textbf{X}^{'}\textbf X \right)^{-1}\textbf{X}^{'}\cdot \textbf Y$$
It can be seen that it is necessary to calculate $\textbf{X}^{'}\textbf X$ and $\textbf{X}^{'}\cdot \textbf Y$ to obtain $\hat{ \beta}$.