Question 1093255
Doors 1 through 9 use {{{ 9 }}}
plates
Doors 10 through 19 use {{{ 2*10 = 20 }}}
plates
Doors 20 through 22 use {{{ 2*3 = 6 }}}
plates
----------------------------------
Total plates used  is {{{ 9 + 20 + 6 = 35 }}}
The total number of doors is {{{ 22 }}}