I am stuck and cannot figure this out! Can you please show the work and explanations?

I am stuck and cannot figure this out! Can you please show the work and explanations? Thank you!

Traffic engineers use systems of equations to study the flow of traffic. The analysis of traffic flow is based on the principle that the number of cars that enter and leave an intersection must be equal. Suppose the traffic flow for some one-way streets can be modeled by the diagram below, where the numbers and the variables represent the numbers of cars entering or leaving an intersection per hour.