Question 992764
Let t = time it takes z to do the job working alone.  Then z works at the rate of 1/t of the job per hour
x works at the rate of 1/10 of the job per hr
y works at the rate of 1/12 of the job per hour
Together x and y works at the rate of 1/10 + 1/12 =12/120 + 10/120=22/120=11/60 of the job per hour
After 1 hour, together they complete (11/60)*1=11/60 of the job leaving 49/60 of the job yet to be done
Soooo, (11/60)*3 + (1/t)*3= 49/60, or
33/60 + 3/t=49/60. multiply each term by 60t
33t + 180=49t
16t=180
t=11.25 hrs
CK 33/60 + 3/11.25 =49/60
99/180 + 48/180 = 147/180
147/180=174/180
Hope this helps ----ptaylor