Ivan has 15 yards of green felt and 12 yards of blue felt to make 3 quilts. If Ivan uses the same
total number of yards for each quilt, how many
yards does he use for each quilt?​

We need 5 yards green felt and 4 yards blue felt for each quilt.

Step-wise:

Let length of green felt be 'x' , length of blue felt be 'y' and and number of quilts be z.

If Ivan has 15 yards of green felt and 12 yards of blue felt to make 3 quilts.

⇒15x+12y=3z15x+12y=3z

Now, divide both sides by 3 , we get

5x+4y=1z5x+4y=1z

Therefore, we need 5 yards green felt and 4 yards blue felt for each quilt.