log help

log ₇ x  +  log ₇ y   -  log ₇ z

Remember that    log a + lg b  = log (a*b)

And

log a - log b  = log (a/b)

So

log ₇ x  +  log ₇ y   =

log ₇ (xy)

And

log ₇ (x y) - log ₇ z  = 

log ₇  ( [xy] / z)