The graph displays the total production cost, in dollars, for manufacturing a certain number of units of a product. The cost includes a fixed setup fee and a variable cost per unit. If the total production cost was $170, how many units were manufactured?

[Graph Description: A line segment starts at (0, 50) and goes up to (100, 250). The x-axis is 'Number of Units' from 0 to 120, with major ticks every 20 units. The y-axis is 'Total Cost ($)' from 0 to 300, with major ticks every 50 units. The line passes through (20, 90), (40, 130), (60, 170), (80, 210).]