Question 1181303
Consider typing a manuscript is 1 job

Carlo takes 10 hours to do the job alone
So he does 1/10 of the job in 1 hour
in the first two hours he does 2/10 of the job ------------A

let bobby take x hours to do the job alpne
so he does 1/x of the job in 1 hour
together they do (1/10 +1/x ) of the job in 1 hour
they work together for4 hours.
so they do 4 (1/10 + 1/x ) job = 4(10+x)/10x =  2(10+x)/5x of the job-----B

Booby works for 6 hours
so he does 6/x of the job -------------C

A+B+c = 1 job

2/10 + 2(10+x)/5x + 6/x =1

Solve for x