Salut!
5)
2(x+5)-x+3(x-1)=35
2x+10-x-3x-3=35
2x-x-3x=35+3-10
-2x=28 / : (-2)
x= - 14
6)
5x+6<31 /-6
5x<25 / : 5
x<5
x∈ℕ => x∈{0,1,2,3,4}
Succes!
