Buying electricity

This task is about adding and multiplying whole numbers and decimals.
 
For businesses the prices for electricity in the city are:
 
 
Day rate:   8.0 cents per unit of electricity

Night rate: 6.3 cents per unit of electricity

a)
A business in the city used 1 500 units at the day rate, plus 1 000 units at the night rate.
What will the cost of electricity be for ...
 
  i)
their day use? $ ______ . ____
 
  ii)
their night use? $ ______ . ____
 
  iii) both their day and night use together? $ ______ . ____
 
 
The prices for electricity for businesses in the country are:
 
 

 

Day rate:   9.0 cents per unit of electricity

Night rate: 6.5 cents per unit of electricity

 
b)
 
A farm used 2 000 units at the day rate, plus 900 units at the night rate.
 
What will this cost them in total? $ ______ . ____