Things you need to know:
[1]color(white)("XXX")log_bp+log_bq = log_b(pq)XXXlogbp+logbq=logb(pq)
[2]color(white)("XXX")log_b m = kXXXlogbm=kcolor(white)("XXXX")XXXX means color(white)("XXX")b^k=mXXXbk=m
log_4 a + log_4 5 = log_4 5a = 3log4a+log45=log45a=3 from [1] and given equality