It says use the substitution method, so you would take the bottom equation, and since it says that x is equal to that, you would use that equation in place of the x in the top equation. so it would be 9y = 3(3y+3) - 9. You then distribute the 3 into the 3y +3, which gets you 9y = 9y + 9 - 9, which is also 9y=9y. Subtract 9y to get 0 = 0, which just means that there are infinite solutions to this equation. Whenever you get 0 = 0, all that means is that there are infinite solutions to this particular set of equations. Hope this helped!
If the first roll is a three, then the only chance of the sum of the two numbers being less than six is if you roll a 1 or a 2. That is 2/6 chance, or simplified, a 1/3 chance.
