Solve
-One Conveyor Belt Can Move 1000 Boxes in 7 $42 \mathrm {~min}$

Multiple Choice

Solve.
-One conveyor belt can move 1000 boxes in 7 minutes. Another can move 1000 boxes in 6 minutes. If another conveyor belt is added and all three are used, the boxes are moved in 3 minutes. How long would it take the third conveyor belt alone to do the same job?

A) $42 \mathrm {~min}$
B) $\frac { 1 } { 42 } \mathrm {~min}$
C) $1 \frac { 5 } { 9 } \mathrm {~min}$
D) $\frac { 9 } { 14 } \mathrm {~min}$