9/4x-1/2y =-3 x and y intercept form

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

Tom can paint the fence in 12 hours, but if he works together with a friend they can finish the job in 8 hours. how long would it take for his friend to paint this fence alone?

Solve the following system of equations express your answer as an ordered pair in the format (a,b) with no spaces between the numbers of symbols 5x+2y=22