The members of a cooking club are making cakes, which they will sell at a street fair for $9 apiece. It cost $50 for a booth at the fair, and the ingredients for each cake cost $4. At some point, the club members will sell enough cakes so that their sales cover their expenditures. How much will the sales and expenditures be?

Assume x to be each piece.

Given:

Sale :They sell at a street fair for $9 a piece. This, can be represented by the expression, 9x.

Expenditure :It costs $50 for a booth at the fair, and the ingredients for each cake costs $4. This can be represented by the equation, 4x + 50.

We write these expression across each other, then we solve for x.

9x = 4x + 50

5x = 50

x = 10.

This means that when the number of pieces are 10, the sales will cover the expenditures.

CHECK:

When x = 10. the amount they get is $90.

When x = 10, the expenditure is 4\cdot 10 + 50 = 90

So, the sales and the expenditure will be the same, when the number of cakes are 10.

Hence proved.

I found an answer from www.reddit.com

[lets build] d100 magic items a travelling witch might sell you : d100

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I found an answer from en.wikipedia.org

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