Solution :
a). [tex]\text{The contribution margin per unit = }[/tex][tex]\text{selling price per unit - variable cost per unit}[/tex]
                              = $ 350 - $ 290
                              = $60
The current break even sales = [tex]$\frac{\text{fixed cost}}{\text{contribution margin per unit}}$[/tex]
                         [tex]$=\frac{780,000}{60}$[/tex]
                         = 13,000 units
Therefore, the current break-even sales (units) = 13,000 units
b). The Contribution Margin Ratio = Selling Price Per Unit - Variable Cost Per Unit
                            = $390 - $290
                           = $ 100
[tex]$\text{Break even sales}=\frac{\text{fixed cost}}{\text{contribution margin per unit}}$[/tex]
             [tex]$=\frac{780,000}{100}$[/tex]
             = 7,800 units.
So, the answer is 7800 units.