Respuesta :

3x+9=36
with 2 times 9kg and 18kg is the solution:

I:2x+y=36
II:y=x+9

if you substitute y of II into I:

3x+9=36
3x=27
x=9
-> 2 boxes with 9kg and 1 with 9+9=18 kg

2*9+18=36kg in total

so the third option/Rashid is the solution