Answer: She made no mistakes
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Reason:
She wants to find the y value when x = 0. This is why she replaced every copy of x with 0. Step 1 is correct.
Step 2 is also correct because 3 times 0 is 0. She multiplied correctly.
Step 3 is correct because she needs to undo the "2 times" that is applied to y, in order to isolate it. Division is the inverse operation of multiplication.
Step 4 is correct because 8/2 is 4
Every step she did is correct, and so is the final answer.
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Here's one way Annabelle could check her work
3x+2y = 8
3*0+2*4 = 8 .... plug in x = 0 and y = 4
0 + 8 = 8
8 = 8
We get the same thing on both sides, which confirms that x = 0 pairs up with y = 4. In other words, (x,y) = (0,4) is a solution to 3x+2y = 8.
The point (0,4) is on the line 3x+2y = 8. This point is the y intercept where the graph crosses the y axis.