Machines P and Q are two different machines that cover jars in a factory. When Machine P works alone, it covers 15 jars in m hours. When Machines P and Q work simultaneously at their respective rates, they cover 15 jars in n hours. In terms of m and n, how many hours does it take Machine Q, working alone at its constant rate, to cover 15jars?	Pick.
A) 15n/225-mn	B) m	C) n	D) m+n	E) M-n
working rate p = 15/m ; working rate pq =( 1/p +1/q)* n =15 or mn/15 +n/q =15 0r n/q = 15-mn/15 = 225-mn/15   q = 15n/225-mn   15n/225-mn
<result>A</result>
Machines P and Q are two different machines that cover jars in a factory. When Machine P works alone, it covers 15 jars in m hours. When Machines P and Q work simultaneously at their respective rates, they cover 15 jars in n hours. In terms of m and n, how many hours does it take Machine Q, working alone at its constant rate, to cover 15jars?