Is this answer correct? the answer i got was -4 is less than or equal to x

It would be correct if it asked for the range, but it's asking for the domain (x values).

The domain of a function excludes imaginary numbers, and you get an imaginary number when x is negative (square root of negative number is imaginary). So x has to be greater than or equal to 0. That's the domain.

Ac equals 35 cm long