Work out the difference (increase) between the two numbers you are comparing.
Increase = New Number - Original Number.
Then: divide the increase by the original number and multiply the answer by 100.
% increase = Increase ÷ Original Number × 100.
So to find the answer you want to isolate the y. So the first thing you want to do is to move everything to the opposite side of the = sign. You start by adding 10 to both sides.
10+ 5y -10 = -25 +10
5y = -15.
the tens cancel out on the left side and on the right you get left with -15/
Since y is being multiplied by 5 you always want to do the opposite so you divide by 5.
5y/5 = -15/5
y = -3
It's hard to explain but you just have to remember that what you do to one side you must do to the other to keep the equation balanced.
I believe it is the SSS postulate because there are two congruent sides and one shared side that they both use.
3x - 4y = 12 ----- (1)
x + 4y = 20 ------ (2)
equation (2) x 3:
3x + 12y = 60 ---(2a)
(2a) - (1):
12y - (-4y) = 60 - 12
12y + 4y = 48
16y = 48
y = 3 ---- sub into equation (2)
x + 4(3) = 20
x + 12 = 20
x = 8
Ans: x = 8 and y = 3 (True)