one machine 10 hours to complete a production order and another machine 20 hours to complete the same order. How many hours would it take both machines working simultaneously at their respective rates to complete the order?	Choose the correct choice.
A) 12/7hrs
B) 20/3hrs
C) 15/6hrs
D) 8/9hrs
E) 15/2hrs
Machine A = 10 hours to complete an order   Machine B = 20hours to complete the same order   We're asked how long it would take the two machines, WORKING TOGETHER, to complete the order.   Using the Work Formula: (A)(B)/(A+B).....   (10)(20)/(10+20) = 20/3 hours to complete the job; Answer is 20/3hrs
<result>B</result>
one machine 10 hours to complete a production order and another machine 20 hours to complete the same order. How many hours would it take both machines working simultaneously at their respective rates to complete the order?