A copy machine, working at a constant rate, makes 25 copies per minute. A second copy machine, working at a constant rate, makes 55 copies per minute. Working together at their respective rates, how many copies do the two machines make in half an hour ?
Choose the correct choice from the following:  A) 90  B) 2,400  C) 4,500  D) 5,400  E) 324,000
Together the two machines make 25+55= 
<gadget id="calculator">25+55</gadget>
<output>80</output>
80 copies per minute. So, in half an hour they will make 80*30=2,400 copies.   Answer: 2,400.
<result>B</result>
A copy machine, working at a constant rate, makes 25 copies per minute. A second copy machine, working at a constant rate, makes 55 copies per minute. Working together at their respective rates, how many copies do the two machines make in half an hour ?