Scenario:   suppose your business makes high-grade pdas, personal digital assistants. it costs you $80,000 a month for fixed costs, such as rent, employee salaries, and other essential items. also, it costs $300 to make each pda, called a unit. if you are able to sell each unit for $500, how many pdas do you need to sell to  break even?
step 1:   set up the variables.
let  x  = the number of units  
y  = the cost/income (expense/revenue) in dollars
step 2:   write cost (expense) and income (revenue) equations.
cost equation:   
total cost = fixed cost +  (cost to make each unit) · (# of units)  
y  =     

income equation:   
total income =     
y  =  
step 3:   solve the system of equations using substitution.
 
step 4:   state the break-even point.