Final answer:
The profit in dollars when 80 units are sold is $70.
Step-by-step explanation:
To calculate the profit when 80 units are sold, we can substitute the value of x = 80 into the equation y = 3.5x - 210. So, y = 3.5(80) - 210 = 280 - 210 = 70.
Therefore, the profit in dollars when 80 units are sold is $70.