A firm has the following cost function, which relates the number of units of an output produced (x) and the cost of producing given quantities of output . Cost is measured in thousands of dollars while output is measured in thousands of units. Given the equation, y= 250 + 0.5x, the cost of producing 1000 more units of output is? O a. $250,500 O b. $1000 c. $250.50 O d. $500