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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