A publisher needs to send many books to a local book retailer and will send the books in a combination of small and large boxes. Each small box can hold 20 books and each large box can hold 45 books. A total of 12 boxes were sent which can hold 340 books altogether. Write a system of equations that could be used to determine the number of small boxes sent and the number of large boxes sent. Define the variables that you use to write the system.

rephrase this open word problem about construction and change the question to solving the linear equation.

A construction company needs to transport a mix of small and large building materials to a job site. Each small container can hold 30 materials, and each large container can hold 50 materials. A total of 10 containers were sent, which can hold 400 materials altogether.

Let x be the number of small containers sent and y be the number of large containers sent. The system of equations to determine the number of small and large containers sent is:

1. 30x + 50y = 400
2. x + y = 10

Now, solve the system of equations to find the number of small and large containers sent.