First, we combine the terms 3y and 6y to get 9y.
We can do this because 3 times a number + 6 times that same number = 9 times that number. To show you this, here's a few examples:
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Let's put some random numbers in. 7 and 4.
(3 x 7) + (6 x 7) = (9 x 7)
21+42 = 63
63 = 63
(3 x 4) + (6 x 4) = (9 x 4)
12 + 24 = 36
36 = 36
Both of these statements are true. This shows us we can do this.
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Back to the question. Let's combine 3y and 6y to get 9y.
10y=3y+10+6y
10y = 9y+10
Now subtract 9y from both sides. We can also do this...I'm not going to show you some examples but you can try it yourself like I did if you'd like
10y = 9y + 10
-9y -9y
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y = 10
And there you go!
