calculate the mass of water used
that is
100-22.2=77.8g convert into Kg = 77.8/1000=0.0778Kg of water
then calculate the moles of HCOOH used
that is 22.2g/molar mass of HCOOH(1+12+16+16+1)=46
therefore the moles of HCOOH=22.2/46=0.48moles
the mole of water= 77.8/18(molar mass of water= 4.32moles
the molarity of HCOOH = 0.48mol/0.0778kg=6.17M
The mole ratio= moles of HCOOH divided by total moles
the total moles= 0.48+4.32=4.8moles
therefore the mole ratio= 0.48/4.8moles=0.1(the moles fraction of HCOOH)