Purpose: to calculate the amount charged for mowing
  a lawn

Preconditions:
need lawn width, lawn length
	house width, house length
	rate of mowing -sq. ft. per hour
	charge per hour
Postconditions:
    output the charge for mowing the lawn

1.  get info about lawn
2.  get info about house
3.  get rate of mowing
4.  find area of house and area of lawn
5.  subtract area of house from area of lawn to get mowing area
6.  calculate number of hours taken to mow by dividing
	mowing area by rate of mowing
7.  calculate total charge by 
	multiplying number of hours by charge per hour
8.  report total charge