a)6432:2:12-1748:2:23+407x2x3=
3216:12-874:23+814x3=
268-38+2442=
230+2442=2672
b){15x13+10[27+10x(407+2405:65)]-4400x10}:5=
{15x13+10[27+10x(407+37)]-4400x10}:5=
{15x13+10[27+10x444]-4400x10}:5=
{15x13+10[27+4440]-4400x10}:5=
{15x13+10x4467-4400x10}:5=
{195+44670-44000}:5=
865:5=173