Question 892417
This solution focuses just on the work time, not on time of the day:


1 job is, "make a card".

RATES of WORK:
Ann, {{{1/10}}}
Bob, {{{1/6}}}
Ann&Bob, {{{1/10+1/6=(6+10)/60=16/60}}}


90 custom cards in this case will mean 90 jobs.
Ann and Bob are to work together to do these 90 jobs.
Time unit will be MINUTES, and you can convert to hours later if you want ( and you will want to ).


Remember, I do not care about the fifteen minute break or start and stop time points in the day.


{{{highlight((16/60)*t=90)}}}.
Solve for {{{highlight_green(t)}}}.