Respuesta :

18/90
Divide by the common factor of 18 and 90, 9.
(18/9) / (90/9)
2/10
Divide top and bottom by 2

1/5

Hope this helps :)
1/5 because  if you divide 18/90 by 2 it is 9/45 thn divide by 9 its 1/5