Question 1003343
 alan, bill, cathy, and debbie work at a sub shop.
let a = Alan's time to make one sub
let b = Bill's time to make one sub
let c = Cathy's time "  "
let d = Debbie's time "  "
:
 It takes alan 2 minutes to make 1 sub alone.
a = 2
 When working together , alan and bill can make 5 subs in 6 minutes,
{{{6/a}}} + {{{6/b}}} = 5
so we have
{{{6/2}}} + {{{6/b}}} = 5
3 + {{{6/b}}} = 5
{{{6/b}}} = 5 - 3
{{{6/b}}} = 2
2b = 6
b = 3 min for bill to make 1 sub
:
 bill and cathy can make 7 subs in 12 mintues, and
{{{12/b}}} + {{{12/c}}} = 7
{{{12/3}}} + {{{12/c}}} = 7
{{{12/c}}} = 7 - 4
{{{12/c}}} = 3
3c = 12
c = 4 min for Cathy to make 1
:
 cathy and debbie can make 9 subs in 20 minutes.
{{{20/c}}} + {{{20/d}}} = 9
{{{20/4}}} + {{{20/d}}} = 9
{{{20/d}}} = 9 - 5
{{{20/d}}} = 4
4d = 20
d = 5 min for Debbie to make 1
:
 If all four employees work together , how many subs can they make in an hour?
All 4 in 60 min
{{{60/a}}} + {{{60/b}}} + {{{60/c}}} + {{{60/d}}} =
replace the values for each 
{{{60/2}}} + {{{60/3}}} + {{{60/4}}} + {{{60/5}}} = 
30 + 20 + 15 + 12 = 77 subs