The sum of (a + b) + c is equal to the sum of a + (b + c) as explained by the blank

1c-2 m405 what values are needed to make each expression a perfect square trinomial? 32 + 2x+ 2-20x + 22+5x+

Anyone know? will mark brainliest if you're correct!

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