Algebra 1-2

3 machines can fill 80 boxes in 2 hours

$(\times\frac53)$                  $(\times\frac{15}{8})$

5 machines to fill 150 boxes in x hours

So look machines are inversely propotional more machines less time but boxes are directly proportional more boxes more time:

$2h.\times\frac35\times\frac{15}{8}=\frac94h.\;(or\;2.25h.)$

Thanks, Solveit....here's another approach....

Three machines fill 40 boxes in one hour.....so one machine fills 1/3 of these in one hour  = 40/3 boxes in one hour

So....one machine would take  150 / (40/3)  =  11.25 hours to fill 150 boxes

So.....five machines would take 1/5 as long =  2.25 hours  .....just as Solveit found!!!!