18(x+5):18x
18x+90:18x
36x+90=441
36x=351
x=9.75
every son will get 9.75+5
14.75
in maths you round up in sharing equations
15
everyone son will get 15 trees
(i’m not sure whether i’ve got this right as i was unsure whether you meant there is 18(sons+grandsons) or 18(sons) and 18(grandsons) hopefully you can just change the equation to suit if it’s wrong :)