Murriel wrote:

Years ago I was told not to use automotive oil in garden tractors and
lawn mowers but rather oil especially formulated for those devices,
such as brands bearing the names "Briggs and Stratton," "Cub Cadet,"
etc.

For four cycle engines use a good synthetic motor oil, I use Mobil 1
5W-30 in all my power equipment. For two cycle engines use a brand name
two cycle oil for the fuel-oil mix.

Now I see that the gasoline at the staion where I deal has 10%
ethanol. Is this acceptable for lawn mowers and garden tractors?

Not really, but you don't really have any other option unless you can
travel to one of the few states where you can get alcohol free gasoline.
To compensate you should put Sta-Bil in all your power equipment fuel,
even if you don't expect to store it that long as the alcoholic fuel
doesn't store well for even short periods.