The numerical coefficients are needed in order to complete the chemical reaction by balancing. Balancing is done by equating the number of atoms/elements on both sides of the chemical reaction. In this item, the balanced chemical reaction is,
3Ca(OH)2 + 2H3PO3 --> Ca3(PO3)2 + 6H2O
The numerical coefficients are 3, 2, 1, and 6.
