Answer:
Revenue Function = 90x
cost function = 50x + 800
Explanation:
given data
sales volume = 600 items
revenues = $54,000
total costs = $20,800
sales volume = 400 items
break-even point = 20 items
solution
first we get here Price per unit for Revenue Function  that is express as
Price per unit  = [tex]\frac{total\ sale}{no\ of unit}[/tex]
Price per unit  = [tex]\frac{54000}{600}[/tex]
Price per unit = Â $90
so here Revenue Function  will be
Revenue Function = 90x  .......................1
here x is sale volume
and
cost function will be
cost function = ax +b   .........................2
here
a is Variable cost per unit  and b is fixed cost  and x is sale function
so when cost at 400 units  will be
$20800 = 400a + b   .......................3
and
Cost at break even point  will be
$90 ×  20 = 20a + b    ..........................4
as here  total cost = total revenue
so from equation 3 and 4 we get a and b
380a = $19000
a = $50
and
b = $20800 - 400 × 50
b = Â $800
so here Cost Function will be from equation 2
cost function = 50x + 800