How would I write the expression as a single logarithm: logbase3(36) - logbase3(4)

Subtraction of logarithms corresponds to division of the numbers themselves.

So log 36 - log 4 = log (36/4) (in any base)

which = log 9

Log 3 (36) - Log 3 (4)
= Log 3 (36/4) ………law of logs
= Log 3 (9)

does this help? and you can simplify this further but you only asked to write as single log.

logbase3(36/4) = logbase3(9)

logbase3(36/4) = logbase3(9)