Shana bought sodas and popcorn for the movies. Sodas cost $3 each and popcorn cost $4 per bag. Shana bought 7 things from the concession, all either sodas or bags of popcorn. Shana spent a total of $26. Write a system of equations involving the number of sodas, s, and the bag of popcorn, b. Solve the system to see how many of each Shana bought.