Salut!
{[7×(2+1)-2×3]÷(1+2)}-[(3×2+5)-10] =
{[7×3-2×3]÷(1+2)}-[(3×2+5)-10] =
[(7×3-2×3)÷3]-[(3×2+5)-10] =
[(21-2×3)÷3]-[(3×2+5)-10] =
[(21-6)÷3]-[(3×2+5)-10] =
(15÷3)-[(3×2+5)-10] =
5-[(3×2+5)-10] =
5-[(6+5)-10] =
5-(11-10) =
5-1 =
4