1. To solve this question, you need to equalize the mass of solute for both solution. The calculation would be:
mass of solute= volume*concentration
mass1=mass2
volume1 * concentration1 = volume2 * concentration2
volume1 * 0.7%= 2L *(1000ml/L) * 0.2%
volume1 = 2000ml * (0.2%/0.7%)
volume1= 571.429 ml
2. Since you already have the volume of stock needed, you just need to subtract it from the total solution volume to count the number of solvents needed.
new solution volume= stock volume + diluting solvent volume
2L * 2000ml/L = 571.429ml + diluting solvent volume
diluting solvent volume= 2000ml- 571.429 ml= 1428.571ml