Serial Computing. Alex bought an MS$-$DOS computer in $1990.$

$($After throwing away MS Windows $3$ from it$.)$

He run two programs. Program A with $100$s CPU time was run first and had also

$50$s I$/$O time immediately following theCPU execution. Then he run Program B with $250$s CPU and $100$s I$/$O following CPU execution.

He started running the programs, A first then B at $09$:$00$:$00.$

What is the completion time of the job $?($Assume $0$ other delays.$)$ Express the answer in format abcdef. Thus a $09$:$40$:$50$ would be written $094050.($And of course it is am$!)$