Factor the following

9t^2-42t+49

  (3t -7)²

Step-by-step explanation:

We know that the square of a binomial is ...

  (a -b)² = a² -2ab +b²

So, when we see the first and last terms are both perfect squares, we suspect that the trinomial is a perfect square trinomial.

  9t² = (3t)²

  49 = 7²

  -42t = -2(3t)(7) . . . . confirming we have a perfect square

The factorization is ...

  (3t -7)²

9 cups of water should be used.
  6 for 4 (flour)
  x for 6 (water)

 Proportion:
 6 - 4         x - 6

Then multiply across
  6 * 6 =4r        36 =4r    
 
 Then divide 36 / 4 = 9

x = 9

 9 cups of water should be used.