1) The identity you need is log(ab) = log(a) + log(b)
log_{2}5+log_{2}8 = log_{2}(8*5) = log_{2}40
2) The identity you need for this one is: log(a^{b}) = b*log(a)
3log_{10}6 = log_{10}(6^{3}) = log_{10}(216)
3) You need to know 2 things: 1000 = 10^{3} and log_{10}(10) = 1
log_{10}(1000) = log_{10}(10^{3}) = 3log_{10}(10) = 3