Question 1173835
first welder,  rate  {{{1/15}}}
second welder, rate {{{1/t}}}
both welders at same time,  {{{1/6}}}



{{{1/15+1/t=1/6}}}

LCD is 30t;

{{{30t(1/15+1/t)=30t(1/6)}}}

{{{2t+30=5t}}}

{{{3t=30}}}

{{{highlight(t=10)}}}