Stan Fawcett's company currently purchases a gear assembly from Salt Lake Supply, Inc., at $$3\mathrm{.}80$ per unit with a minimum order of $3,000$ units. Stan is considering instead producing the gear assembly himself. He estimates that producing it himself will cost $$15,000$ to set up the process and then $$2\mathrm{.}00$ per unit for labor and materials.

a$)$ Using the line drawing tool, add the total cost graph for Stan to produce the assembly instead of purchasing from Salt Lake Supply. Total cost for the purchase option is already plotted. Properly label your line.

Note: Carefully follow the instructions above and only draw the required object.

b$)$ The number of units at which either choice has the same cost is $($round your response to the nearest whole number$).$

Please explain using formulas and step$-$by$-$step instructions