During a store's opening month, they sold 925 DVD's and 507 Blu-ray discs. Each month thereafter, the number of DVD's sold per month decreased by 12 while the number of Blu-ray discs sold per month increased by 26. Let d represent the number of discs sold and t represent the time in months. Write a system of equations

Solve the system of equations using the substitution method. Complete the sentence to describe the solution.