The solution of a system of 1st degree equations with two unknowns is the ordered pair that satisfies both equations at the same time.
Look at the example:
Equation solutions x + y = 7 (1,6); (2,5); (3,4); (4,3); (5,2); (6,1); etc.
Equation solutions 2x + 4y = 22 (1,5); (3,4); (5,3); (7,2); etc.
The ordered pair (3,4) is the solution of the system, as it satisfies both equations at the same time.
Let's graph the two equations and check if the intersection of the lines will be the ordered pair (3,4). 
Therefore, we can verify through the graphical construction that the solution of the 1st degree equation system with two unknowns is the intersection point of the two lines corresponding to the two equations.
Example 2
Claudio used only R$20.00 and R$5.00 bills to make a payment of R$140.00. How many notes of each type did he use, knowing that in total there were 10 notes?
x 20 reais bills and 5 reais bills
system of equations 
We can verify through the graphical representation that the solution of the 1st degree system of equations is x = 6 and y = 4. Ordered pair (6.4).
by Mark Noah
Graduated in Mathematics
Brazil School Team
Equation - Math - Brazil School
Source: Brazil School - https://brasilescola.uol.com.br/matematica/solucao-um-sistema-equacoes-1-grau-com-duas-incognitas-.htm