The cost of renting tuxes for the Choral Society's formal is $20 down, plus $80 per tux. Express the cost C as a function of x, the number of tuxedos rented.

C = 80 x + 20

To express the cost, C, as a function of the number of tuxedos rented, x, we need to consider both the down payment and the cost per tuxedo.

The down payment for renting tuxedos is $20, which is a fixed cost that does not depend on the number of tuxedos rented. So, the down payment, D, is equal to $20.

The cost per tuxedo rented is $80. This cost is multiplied by the number of tuxedos rented, x, because the total cost will depend on how many tuxedos are rented. So, we multiply $80 by x.

Therefore, the cost, C, can be expressed as the sum of the down payment, D, and the cost per tuxedo rented, which is $80 multiplied by x:

C(x) = D + ($80 * x)

Substituting the values:

C(x) = $20 + ($80 * x)

So, the cost of renting tuxedos, C, is a function of x, the number of tuxedos rented, and can be expressed as C(x) = $20 + ($80 * x).