JEE Mains Model Paper 13

Apatite is a mineral that is found in tooth enamel when fluoride toothpastes are used, thismineral is converted to fluoroapatite which is more resistant to tooth decay the formula ofapatite is Ca2(PO4)xF. What is the value of X if the compound contains 18.45% by weight ofphosphorous (At.wts.of P = 31, Ca=40, F=19, O = 16)