Welcome to MHF! Please post only one question per thread in the future.
I am assuming by "log" you mean . In higher math, this can mean so be careful and specific.
I'll help with your second question. Notice that log(x) has a real domain for x>0, not including 0. So use that to make some deductions. Firstly, 0.5x-3 > 0 for this to work but also log(0.5x-3) > 0 so that log(y) is defined. For what values of "a" is log(a) negative?