Question 661572
Let {{{ t }}} = the time in hrs it 
takes Lia to paint the floor
{{{ t + 3 }}} = time it takes Zeno
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Add their rates of working to get their
rate working together
( 1 floor painted / Zeno's time ) + ( 1 floor painted ) / ( Lia's time )
= ( 1 floor painted ) / ( time for both painting together )
{{{ 1/(t+3) + 1/t = 1/2 }}}
Multiply both sides by {{{ 2*t*( t + 3 ) }}}
{{{ 2t + 2*( t + 3 ) = t*( t + 3 ) }}}
{{{ 2t + 2t + 6 = t^2 + 3t }}}
{{{ t^2 - t - 6 = 0 }}}
I can see that this is
{{{ ( t - 3 )*( t + 2 ) = 0 }}}
{{{ t = 3 }}} 
( can't be {{{ t = -2 }}} because you can't have negative time )
and
{{{ t + 3 = 6 }}}
Lia takes 3 hrs to paint the floor
Zeno takes 6 hrs to paint the floor
check answer:
{{{ 1/(t+3) + 1/t = 1/2 }}}
{{{ 1/(3+3) + 1/3 = 1/2 }}}
{{{ 1/6 + 2/6 = 3/6 }}}
{{{ 3/6 = 3/6 }}}
OK