in Excel 2003, I use the following equations to calculate the cost of the electricity consumption. I have to use different equations for different consumption slice situations.

The next figure shows the data used for consumption slices and the cost for each slice:

I put fixed values in cells and refer to them. For example: 0.5 in cell A1 0.82 in cell B1 1 in cell C1

in October the consumption was 190 kwh,

I used the equation =((190*$A$1))+6

in December the consumption was 228 kwh,

I used the equation =((200*$A$1)+(28*$B$1))+11

in August the consumption was 370 kwh,

I used the equation =((200*$A$1)+(150*$B$1)+(20*$C$1))+15

How to use one equation in all the different consumption slice situations, instead of using different equations in different situations.