Xia and Yvonne collect buttons. Xia has 10 more buttons than Yvonne. How many buttons do they have

Xia only collects the ones with two holes, and Yvonne only collects the ones with four holes.
The total number of holes found in all of their buttons is 200.

Let Xia's number of button be X
Let Yvonne's number of button be Y

Relationships of X and Y are:

1. 2X+4Y=200

2. X = 10 + Y

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Substitute value of X in (2.) into (1.), we get
2(10+Y)+4Y=200
20+2Y+4Y=200
6Y=180
Y=30 (Yvonne has 30 4-holes-button)

What about Xia? Refer to (2.) X=10 + Y
X=10+30
X=40 (Xia has 40 2-holes-button)

Answer: Y=30, X=40

Hope it helps.