Not really sure if the question links well with the problems
for the first one you can factor out the half in each term then use the identity for subtracting logs
Without knowing what a, b, and c are, or at least what log(a) and log(b) are, I cannot imagine how you could write
"(1/2)log(80)- (1/2)log(5)" "in terms of log(a) and log(b)".
It is certainly true that (1/2)log(80)- (1/2)log(5)= (1/2)log(80/5)= (1/2)log(16)= log(4) but, again, how is that connected to a and b?