An Algebra Problem - Please, please help. Soon, possibly?

Question

A utility company charges $15 for the first 100 kilowatt-hours of electricity used by a household each month, and $0.15 for each kilowatt-hour over 100. Let n = the number of kilowatt-hours used by a household (n > 100). Write a variable expression for the amount charged.

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Simply, I don't have any idea what to do.

Answer 1

You start with the 15.  Then you add in 0.15 for every hour over 100.  If you think "over 100", subtraction should suggest itself.  So:

amount = 15 + 0.15(n - 100)

Edit:  You only have two answers, luv.  Mine and the one after mine are equivalent.  The first one is almost right but left out the "- 100".  With that in mind, use any of them.

Answer 2

Since you only need an expression, rather than a solvable equation, you can write:

Let n = kilowatt-hours used. Then, the dollar-amount charged can be expressed as:

$15. + $0.15n; n > 100

$15.; n </= 100

If you need an equation, which you cannot solve if it has two unknowns, you can write:

Let C = dollar amount charged, and n = kilowatt-hours used. Then,

C = $15. + $0.15n; n > 100

C = $15.; n </= 100

Answer 3

y = 0.15(n - 100) + 15 ,  

Answer 4

15 + 0.15n = amount charged