The correct option is A 43
Base of third number is the product of bases of first and second number.
∴ Base of third number is
6×7=42
Base of resultant square number is related to the base of the third square number. The base of the resultant square number is the number next to the base of the third number.
∴ The base of the resultant square number is the number next to 42 i.e. 43.