Concentrate is mass (M) divided by volume (V). Volume is measured in litres, cc or ml, etc., while mass is grams, mg, microgram, etc. 48.6 is a concentrate (C) of ml divided by mg (I assume) and you have to find V knowing C=48.6 and M=50. M/V=C so M=VC and V=M/C=50/48.6=1.029ml approx. I have assumed that concentrate is measured in mg per ml, if it's mg per litre then the answer would be 1.029 litre or 1029ml. If concentrate is microgram/ml, then M=50000 microgm, so V would be 1029ml. You will know which answer is most sensible.