Let's say the factory produces x widgets per day. (We could choose any meaningful variable - n would also be a good choice.)

The daily total cost C equals the fixed cost of `$50,000` plus the variable cost of producing x units.

The cost of producing 1 unit is `$10`, so the cost of producing x units is `$10x`.

So the total cost C, where C is a function of x is

`C(x) = 50000 + 10x `

For example, the daily cost of making `2000` widgets is:

`C(2000)` ` = 50000 + 10 × 2000` ` = $70,000 `

Note that in this example, x can only take integer values of `0` or more (we can't make negative widgets).

The lowest cost is `$50,000` per day, when we make `0` widgets.

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