Question 428211
You have to add their rates of mowing
In words:
( 1 lawn) / (Jack's time to mow it) + (1 lawn ) / (Marilyn's time to mow it) = 
{1 lawn) / (Their time mowing it together)
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given:
Jack's rate  = {{{1/8}}} lawns/hour
Marilyn's rate = {{{1/6}}} lawns/hour
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{{{ 1/8 + 1/6 = 1/t }}}
Multiply both sides by {{{24t}}}
{{{ 3t + 4t = 24 }}}
{{{ 7t = 24 }}}
{{{ t = 3.43 }}} hrs 
or, about 3 hours and 26 minutes