How do you simplify log 4 + log 5 - log 2?

To answer this question, the following logarithm rules are needed:
loga+logb = log(a*b)
loga - logb = log(a/b)
log_b b = 1

Using the above rules:
log4 + log5 - log2
=log((4*5)/2)
= log(20/2)
= log(10)
Since the base of a normal log is 10, log10 = 1 (come 10^1 = 10).