[This problem is the same as answering: `3^?= 8.7`].

We cannot find `log_3 8.7` on a calculator. We need to use the change of base formula.

In this case, `b = 3` and `x = 8.7`.

So

`log_3\ 8.7=(log_10 8.7)/(log_10 3)` `=0.9395192/0.4771212` `=1.9691414`

CHECK: By calculator, `3^1.9691414 = 8.6999989`.

[We could have used natural logs as well, `log_3\ 8.7=(ln\ 8.7)/(ln\ 3)` which will give us the same answer.]