These appear to be homework questions. You should post in the Homework Help forum so someone doesn't just give you the answers; which likely be considered cheating. Whether you get help quickly will depend on you.
actuality this is not a home work, this is a practice test, and tomorrow i have final test . just i want to know how i can figure this out
Practice test, homework; little difference. Post your work. Hopefully any responders will try to guide you to a solution instead of simply giving you the answers.
MOD NOTE: Moved from General Electronics Chat to Homework Help. @Hossam Saleh : You need to post your best attempt at answering these questions. That will let us provide better feedback on what you are doing right and where you are going astray.
Check your arithmetic for calculating parallel resistance. 1K in parallel with 2 larger resistances can't be larger than 1K.
You need to learn to track your units. You start out with R = 1/R1 + ... Right off the bat you have an equation guaranteed to produce the wrong result. The units on the left are resistance and on the right are conductance. Tracking your units would have revealed this. Then you express R123 in amps? Take your time and stop being so sloppy. It will save you time and effort in the long run.