25/10 as a mixed number

There are 15 plates and each plate is either 7 or 12 inches diameter. which systems of equations do you use to find the number of 7 inch plates, x and 12 inch plates, y

Ineed in figuring out this problem.

Two times a number plus three times another number equals 4. three times the first number plus four times the other number is 7. find the numbers