The expression that can be used to model the phrase "the sum of three and a number" is:
3 + x
However, from the given options, it seems none directly match this. If you're referring to a notation where "0" might stand for a zero or another term, it looks like an error in formatting. Based on common mathematical conventions, "03+x" (interpreting "03" as just "3") would be correct if we assume leading zeros are not significant.
So, the best interpretation from the given options would be:
03+x (assuming it represents 3 + x).