The required polynomial can be obtained by subtracting the polynomial 4m + 2n + 3 from 6m + 3n + 10.
∴ Required polynomial
= (6m + 3n + 10) − (4m + 2n + 3)
= 6m + 3n + 10 − 4m − 2n − 3
= 6m − 4m + 3n − 2n + 10 − 3
= 2m + n + 7
Thus, the polynomial 2m + n + 7 is to be added to 4m + 2n + 3 to get the polynomial 6m + 3n + 10.