one clerk can stuff every 30 seconds the 2nd clerk i every 40 seconds. how long will it take them to stuff 140 envelopes

Answer 1

1/30 = .033 envelopes/sec
1/40 = .025 envelopes/sec
so
.033+.025 = .058 envelopes /sec together
1/.058 = 17.2 seconds/envelope
140 envelopes * 17.2 seconds/envelope = 2413 seconds or 40 minutes