15)
{[23×(48÷6×2-4+2)÷2]÷2+4}÷3-3=
={[23×(8×2-4+2)÷2]÷2+4}÷3-3=
={[23×(16-4+2)÷2]÷2+4}÷3-3=
=[(23×14÷2)÷2+4]÷3-3=
=[(322÷2)÷2+4]÷3-3=
=(160÷2+4)÷3-3=
=(80+4)÷3-3=
=84÷3-3=
=28-3=
=25
16)
3×{3+3×[3+3×(3+3)]+3×3^2}=
=3×[3+3×(3+3×6)+3×9]=
=3×[3+3×(3+18)+3×9]=
=3×(3+3×21+3×9)=
=3×(3+63+27)=
=3×(66+27)=
=3×93=
=279
17)
[5×(12-2×5)÷2]^2=
=[5×(12-10)÷2]^2=
=(5×2÷2)^2=
=(10÷2)^2=
=5^2=
=25
