figuring out a percentage function

Sorry, guys. I actually dont even know how to do this mathematically or else i would be able to figure it out on excel.
But I am a subcontractor that is under another subcontractor. when I get done with a job, the employers above me pay, the guy above me, he then takes out 30% and gives me the rest.
If i know how much I am getting, but dont know how much my boss made, how would i do that with excel.
so say in A1 i have $3178 (my check amount) and i know that my boss took 30% of the orginal, what equation would I put in A2 to figure out what He profited

awesome, that worked. Thank you