Question 1122410
In 8 min, Shelly stocks {{{ 23*8 = 184 }}} cans
There are {{{ 500 - 184 = 316 }}} cans left to stock
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Let {{{ t }}} = time for them to finish working 
Add their rates of working to get their rate working together
{{{ 17 + 23 = 316/t }}}
{{{ 40 = 316/t }}}
{{{ t = 7.9 }}} min
It takes them 7.9 min to stock the rest of the cans