Questions about Multi linear regression model.

I have two questions about multi linear regression model.

First question. Suppose 2 independent samples

Sample1 : $y_1$, ... $y_{n_1}$ and $x_1$, ..., $x_{n_1}$

Sample2 : $y_{n_1 +1}$, ... $y_{n_1 +n_2}$ and $x_{n_1 +1}$, ..., $x_{n_1 +n_2}$

and each samples fit in the models as follows :

Sample 1 : $y_i$ = $\beta_0$ + $\beta_1$$x_i + \epsilon for i = 1,2,...,n_1 Sample 2 : y_i = \gamma_0 + \gamma_1$$x_i$ + $\epsilon$ for i = $n_1 +1$,...,$n_1+n_2$

I want to unite these two models into a single model. How can i do this? I have considered a multi linear regression model with two regressor x and x' where x is from sample1, x' is from sample2. but I can't deal with the constant part.

Second question.